Safety Assessment of Hydrogen Peroxide as Used in Cosmetics

Definition and Structure

Hydrogen Peroxide is the inorganic oxide that conforms to the structure in Figure 1. ¹ OPEN IN VIEWER

Chemical Properties

Chemical properties of Hydrogen Peroxide are presented in Table 1. Pure Hydrogen Peroxide (100%) does not exist commercially, and is only of academic interest.^6,7 Hydrogen Peroxide is always manufactured as an aqueous (aq.) solution and is supplied commercially at concentrations of 3% to 98% Hydrogen Peroxide. ⁸ Pure Hydrogen Peroxide is a crystalline solid below 12 °F (−11.11°C) and a colorless liquid with a bitter taste above 12 °F. ⁹ Hydrogen Peroxide can behave both as an oxidizing agent and as a reducing agent.

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Table 1.

Chemical and Physical Properties of Hydrogen Peroxide (100%).

Property	Value	Reference
Physical Form	Liquid	5,136,137
Color	Colorless	5,136,137
Odor	Sharp	5,137
Taste	Bitter	9
Molecular Weight (g/mol)	34.02	2
Density (g/mL) @ −20°C @ 25°C	1.17	2
	1.4425	11
Viscosity (kg/(s*m) @ 20°C)	0.001249	2
Vapor pressure (mmHg @ 30°C)	5	9
Melting Point (oC)	−11.11	9
Boiling Point (oC)	150.2	2
	150–152	11
	141	9
Water Solubility (g/l @ 20°C & pH 7)	100	2
	Miscible	11,13
log Pow	−1.57 est.	2
Disassociation constants pKa (@ 25°C)	11.62 est.	2,11

Aqueous solutions containing 35, 5, 70, or 90% Hydrogen Peroxide are the most commonly used solutions for industrial applications and in laboratory settings, and require a stabilizer (commonly acetanilide) to prevent rapid decomposition to water and molecular oxygen. Aqueous solutions of 3 to 6% are used for cosmetic and medical applications.

Hydrogen Peroxide and water do not form an azeotropic mixture (two or more liquids whose proportions cannot be altered or changed by simple distillation), and are completely separable. ⁶ The dissociation of Hydrogen Peroxide can be a violent and exothermic reaction.^9,10 Hydrogen Peroxide is nonflammable, but it is a powerful oxidizing agent that can accelerate combustion when it comes in contact with organic material. Aqueous solutions of Hydrogen Peroxide, at low concentrations in clean inert containers, are relatively stable. ⁸ Stability is at a maximum in mildly acidic solutions between pH 3.5 to 4.5.

Natural Occurrence

The concentration of Hydrogen Peroxide in the environment results from a dynamic equilibrium between its production and degradation. ¹¹ Hydrogen Peroxide may be formed in photochemical, chemical, or biochemical processes.

Hydrogen Peroxide is produced metabolically in intact cells and tissues. ⁸ It is formed by reduction of oxygen either directly in a two-electron transfer reaction, often catalyzed by flavoproteins, or via an initial one-electron step to a superoxide anion, followed by dismutation to Hydrogen Peroxide.

Method of Manufacture

Hydrogen Peroxide can be manufactured by anthraquinone autoxidation. ¹¹ The anthraquinone derivate is hydrogenated to corresponding anthrahydroquinone using a palladium or nickel catalyst. Hydrogen Peroxide is formed when anthrahydroquinone solution is oxidized back to anthraquinone by bubbling air or oxygen through the solution. Crude Hydrogen Peroxide is extracted with water from the organic solution and the redox cycle is repeated with the generation of additional Hydrogen Peroxide. The extracted crude aqueous solution contains approximately 20 to 40% Hydrogen Peroxide and is normally purified in two or three stages by extraction with organic solvent. Finally, the aqueous solution is concentrated to give 50 to 70% Hydrogen Peroxide solutions.

Several other methods of manufacture have been reported. Hydrogen Peroxide can be manufactured by the electrolytic oxidation of sulfuric acid or a sulfate to persulfuric acid or a persulfuric acid salt with subsequent hydrolysis and distillation of the Hydrogen Peroxide that is formed; by decomposition of barium peroxide with sulfuric or phosphoric acid; by hydrogen reduction of 2-ethylanthraquinone, followed by oxidation with air, to regenerate the quinone and produce Hydrogen Peroxide; or by electrical discharge through a mixture of hydrogen, oxygen, and water vapor. [21CFR184.1366]

High concentration commercial Hydrogen Peroxide grades are stabilized to prevent or slow down decomposition and prevent possibly violent decomposition due to catalytic impurities or elevated temperatures and pressure.^6,11 The stabilizers are of several types: mineral acids to keep the solution acidic (stability is at a maximum at pH 3.5 to 4.5); complexing/chelating agents to inhibit metal-catalyzed decomposition; or colloidal agents to neutralize small amounts of catalysts or adsorb/absorb impurities. The types of stabilizers used in Hydrogen Peroxide vary between producers and product grades and may have additional purposes. ¹² For example, nitrate (sodium and ammonium) is used for pH adjustment and corrosion inhibition, and phosphoric acid is also used for pH adjustment. Colloidal silicate is used to sequester metals and thereby minimize Hydrogen Peroxide decomposition in certain applications that depend on the bleaching ability of Hydrogen Peroxide in alkali. In some applications, a high degree of stabilization is needed; whereas, in others (e.g., drinking water treatment or semiconductor manufacture) product purity is more important.

When added to final cosmetic formulations, ingredients, including stabilizers, are listed on the labels of Hydrogen Peroxide-containing hair dyes and cosmetics. However, stabilizers may be utilized in the production of concentrated raw materials (e.g., to stabilize a 30% industrial solution prior to dilution for cosmetic use). Although such a raw material stabilizer would be significantly diluted for use as a cosmetic ingredient, and even further diluted when formulated into a final cosmetic product or hair dye, some residual/incidental concentration may remain and not appear on the label. A list of stabilizers that have been reported for use in the commercial production of aqueous Hydrogen Peroxide is presented in Table 2. In the European Union (EU), concentrated Hydrogen Peroxide that comes in contact with food is stabilized with a tin-based stabilizer. ¹³

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Table 2.

Chemicals Used to Stabilize Aqueous Hydrogen Peroxide. ¹¹

Phosphoric Acid	Sodium phosphate	Sodium stannate
Ammonium sulfate	Sodium silicate	Acetanilide
8-Hydroxyquinoline	Pyridine carboxylic acid	Benzoic acids
Nitrate salts

Impurities

In the US, to meet the requirements of the Food Chemicals Codex, 30 to 50% aqueous solutions of Hydrogen Peroxide must pass an identification test and meet the following specifications: acidity (as sulfuric acid), 0.03% max; phosphate, 0.005% max; lead, 0.0004% max; tin, 0.001% max; and iron, 0.00005% max. ¹⁴

In commercial Hydrogen Peroxide manufactured for the purposes of medical and food biocides in Finland, none of the reported impurities were at concentrations greater than 0.1%. ⁶ The sum of organic and inorganic impurities in aqueous solution is reported to be below 0.2 w/w %. Calculated from a 35% aqueous solution of Hydrogen Peroxide, the theoretical total impurity contents is below 0.5 w/w %. In biocidal products, heavy metals in aqueous Hydrogen Peroxide are limited to a maximum of 1 mg/kg each of lead, mercury, cadmium, and arsenic.

Cosmetic

The safety of the cosmetic ingredient included in this assessment is evaluated based on data received from the US Food and Drug Administration (FDA) and the cosmetic industry on the expected use of this ingredient in cosmetics. Use frequencies of individual ingredients in cosmetics are collected from manufacturers and reported by cosmetic product category in FDA’s Voluntary Cosmetic Registration Program (VCRP) database. Use concentration data are submitted by the cosmetic industry in response to surveys, conducted by the Personal Care Products Council (Council), of maximum reported use concentration by product category.

According to VCRP survey data received in 2018, Hydrogen Peroxide is reported to be used in 390 formulations (18 leave-on products and 372 rinse-off products; Table 3). ¹⁵ The majority of these uses are in hair coloring formulations (250 uses) and in products that may be incidentally ingested (93 oral hygiene products).

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Table 3.

Frequency of Use According to Duration and Exposure of Hydrogen Peroxide.^15,16.

Use type	Uses	Maximum Concentration (%)
Total/range	390	0.000002–15
Duration of use
Leave-on	18	0.000002–4
Rinse-off	372	0.000003–15
Diluted for (bath) use	NR	NR
Exposure type
Eye area	NR	0.000002
Incidental ingestion	93	1.5–4.6 (in oral hygiene products)
Incidental Inhalation-sprays	2; 5a	4; 0.01–2 a
Incidental inhalation-powders	NR	0.000002 b
Dermal contact	11	0.000002–3
Deodorant (underarm)	NR	NR
Hair-noncoloring	33	0.00008–4
Hair-coloring	250	3.5–15 c
Nail	3	NR
Mucous Membrane	93	0.00009–4.6
Baby	NR	0.0019

The results of the concentration of use survey conducted by the Council in 2017 indicate that Hydrogen Peroxide is used at a maximum concentration of 15%; this use is in the category of “other” hair coloring preparations. ¹⁶ The product that contains 15% Hydrogen Peroxide is a professional 50 volume developer, and standard dilutions include 10, 20, 30, and 40 volume (i.e., 3, 6, 9, and 12% Hydrogen Peroxide, respectively).

The highest maximum concentration of use reported in hair dyes and colors is 12.4%. ¹⁶ Permanent hair dyes, also called oxidative dyes, are the most common type of hair dye. ¹⁷ The hair is dyed by oxidation of precursors which penetrate the hair fiber, where they react with Hydrogen Peroxide to produce dyes. Since Hydrogen Peroxide is an excellent decolorizing agent for melanin, the hair’s natural coloring matter, manufacturers can balance the amounts of Hydrogen Peroxide and of dye precursors in such a way as to produce lightening, darkening, or matching of the natural color of the hair.

According to the Council survey, Hydrogen Peroxide is being used at up to 12% in hair bleaches. ¹⁶ Hair bleaching methods are oxidative processes, ¹⁷ and Hydrogen Peroxide is the most common oxidant used in hair bleaching. Hydrogen Peroxide can be used alone to bleach hair, but in hairdressing salons, it is mixed with an alkaline solution, typically comprising aqueous ammonia (in part), before use in order to accelerate the process.

When using hair dyes or relaxers, the FDA recommends that consumers follow all directions in the package, perform a 48-h patch test on the skin before using the dye on hair, wear gloves, and rinse the scalp well with water after use. ¹⁸ Consumers should not dye eyebrows or eyelashes, or leave the product on longer than the directions say. For more information, the FDA’s informational website is https://www.fda.gov/forconsumers/byaudience/forwomen/ucm118527.htm.

Hydrogen Peroxide is also used in products that can result in incidental oral ingestion; the highest reported maximum concentration of use in oral hygiene formulations is in dentifrices at up to 4.6%. Formulations containing Hydrogen Peroxide can come in contact with the skin, and the maximum concentration of use for leave-on dermal exposure is 2.5% in “other skin care preparations.” Hydrogen Peroxide is also reported to be used in the category of baby lotions, oils and creams at up to 0.0019% and in formulations that are used near the eyes at up to 0.000002% (eye lotions).

Additionally, Hydrogen Peroxide is used in cosmetic sprays and could possibly be inhaled; for example, it is reported to be used at up to 4% in aerosol hair sprays. In practice, 95 to 99% of the droplets/particles released from cosmetic sprays have aerodynamic equivalent diameters >10 μm, with propellant sprays yielding a greater fraction of droplets/particles <10 μm compared with pump sprays.^19,20 Therefore, most droplets/particles incidentally inhaled from cosmetic sprays would be deposited in the nasopharyngeal and thoracic regions of the respiratory tract and would not be respirable (i.e., they would not enter the lungs) to any appreciable amount.^21,22

The European Commission (EC) restricts the amount of Hydrogen Peroxide that may be present in cosmetic products (Table 4). ²³ These restrictions included a maximum concentration of 4% in products applied to skin and 12% in products applied to the hair; dyes that are intended to be used on eyelashes (professional use only) are safe when they contain up to 2% Hydrogen Peroxide. ²⁴

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Table 4.

EU Restrictions for Hydrogen Peroxide in Cosmetic Products.^23,24

Product type	Label Instructions/Warnings	Maximum concentration
Hair	Wear suitable gloves. Contains Hydrogen Peroxide. Avoid contact with eyes. Rinse eyes immediately if product comes into contact with them.	12% present or released
Skin	Contains Hydrogen Peroxide. Avoid contact with eyes. Rinse eyes immediately if product comes into contact with them.	4% present or released
Nail hardening	Contains Hydrogen Peroxide. Avoid contact with eyes. Rinse eyes immediately if product comes into contact with them.	2% present or released
Oral products including mouth rinse, tooth paste, and tooth whitening/bleaching products		≤0.1% present or released
Tooth whitening or bleaching (to be only sold to dental practitioners)	Contains Hydrogen Peroxide.Avoid contact with eyes.Rinse eyes immediately if product comes into contact with them.Concentration of Hydrogen Peroxide. Not to be used on a person under 18 years of age.To be sold only to dental practitioners. For each cycle of use, the first use to be only done by dental practitioners or under their direct supervision if an equivalent level of safety is ensured. Afterwards to be provided to the consumer to complete the cycle of use.	>0.1% to ≤6%
Eye lashes; professional use only	Wear suitable gloves.For professional use only.Avoid contact with eyes.Rinse eyes immediately if product comes into contact with them.Contains Hydrogen Peroxide.	2% present or released

Limits for Hydrogen Peroxide in oral care products are included in European Union (EU) cosmetic regulations ²⁵ ; an SCCP opinion formed the basis of these limits. ³ According to Part 1 of Annex III to Directive 76/768/EEC, the maximum authorized concentration of Hydrogen Peroxide in finished oral products in the EU, including mouth rinse, tooth paste and tooth whitening or bleaching products, is ≤ 0.1% (present or released). ²⁵ In addition, tooth whitening or bleaching products containing more than 0.1%, but less than 6%, Hydrogen Peroxide should only be sold to dental practitioners and used by those over the age of 18. Based on a no-observable-adverse-effects level (NOAEL) of 20 mg/kg/day (Hydrogen Peroxide (concentration not specified) in a 100-day rat gavage study and an estimated daily exposure to toothpaste of 480 mg/day Hydrogen Peroxide (0.1% aq.)), the estimated margin of safety (MOS) was calculated to be 2500. ³ Based on an estimated daily exposure to mouth-rinse of 3000 mg/day Hydrogen Peroxide, the MOS was calculated to be 400.

NICNAS conducted a Tier II assessment (evaluation of risk on a substance-by-substance or chemical category-by-category basis) on Hydrogen Peroxide under the Multi-tiered Assessment and Prioritisation Framework (IMAP). ⁵ In that assessment, it was noted that Hydrogen Peroxide, in hair dyes containing 3, 6, or 12% Hydrogen Peroxide, is both a Schedule 5 (caution – substances with a low potential for causing harm, the extent of which can be reduced through the use of appropriate packaging with simple warnings and safety directions on the label) and a Schedule 6 (poison – substances with a moderate potential for causing harm, the extent of which can be reduced through the use of distinctive packaging with strong warnings and safety directions on the label) substance, according to the Australian Government Poisons Standards. ²⁶ It is advised that consumers using products containing Hydrogen Peroxide follow the directions on the label to avoid harm.

Non-Cosmetic

Food

Regulations for uses of Hydrogen Peroxide are presented in Table 5.

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Table 5.

U.S. FDA and EPA Regulations on Hydrogen Peroxide in Food Preparation.

Permitted use	Regulation
Up to 23 mg/kg may be used in a silver nitrate solution as an antimicrobial agent in bottled water	21CFR172.167
As part of a solution to make acetone peroxides to use as bleaching agents in flour or a dough conditioning agent in rolls and breads	21CFR172.182
With lecithin, as hydroxylated lecithin, as an emulsifier in foods	21CFR172.814
Food starch may be bleached with Hydrogen Peroxide if active oxygen from Hydrogen Peroxide does not exceed 0.45% all active oxygen	21CFR172.892
With acetic acid to form peroxyacetic acid up to 59 ppm may be used in wash water on fruits and vegetables that are not raw in combination	21CFR173.315
Epoxidize soybean oil by reacting soybean oil in toluene with hydrogen peroxide and formic acid	21CFR172.723
Used in adhesives that come in contact with food	21CFR175.105
The sterilization of polymeric food-contact surfaces (e.g., food packaging materials)	21CFR178.1005
An aqueous solution containing Hydrogen Peroxide, peracetic acid, acetic acid, and 1-hydroxyethylidene-1,1-diphosphonic acid may be safely used on food-processing equipment and utensils, and on other food-contact articles to control the growth of micro-organisms	21CFR178.1010
Used as ingredients in an antimicrobial pesticide formulation, may be applied to food-contact surfaces in public eating places, dairy-processing equipment, and food-processing equipment and utensils; when it is ready for use, the end-use concentration is not to exceed 91 ppm Hydrogen Peroxide	40CFR180.940

EPA = Environmental Protection Agency; FDA = Food and Drug Administration.

In the US, the FDA recognizes Hydrogen Peroxide as generally recognized as safe (GRAS) to treat food under specific conditions outlined in the Code of Federal Regulations (CFR); maximum treatment levels range from 0.04% to 1.25%, or as an amount sufficient for the purpose. [21CFR184.1366] Hydrogen Peroxide may be used in several capacities in food preparation (bleaching agent, emulsifier, epoxidizing agent). [21CFR172.182, 21CFR172.814, 21CFR172.892, 21CFR172.723] It may be used in adhesives that come in contact with food. [21CFR175.105] Hydrogen Peroxide is also permitted to be used as an antimicrobial agent in bottled water (in a silver nitrate solution), to sterilize food-contact surfaces, and in solutions to clean food-processing equipment and utensils. [21CFR172.723, 21CFR178.1005]

The US Environmental Protection Agency (EPA) stipulates that Hydrogen Peroxide, when used as an ingredient in an antimicrobial pesticide formulation, may be applied to food-contact surfaces in public eating places, and food-processing equipment and utensils; when it is ready for use, the end-use concentration is not to exceed 91 ppm (0.0091%) Hydrogen Peroxide. [40CFR180.940]

Hydrogen Peroxide (not to exceed 200 ppm; 0.02%) is used to reduce the bisulfite aldehyde complex in distilling materials for processing spirits. [27CFR24.247]

Dermal Penetration

Hydrogen Peroxide is reactive, and degrades rapidly, due to reactions with all classes of organic biomolecules. ⁶ The rapid degradation upon contact with skin explains the absence of systemic effects from dermal exposure to Hydrogen Peroxide. However, it is possible that application of Hydrogen Peroxide solutions to damaged skin, or exceptional cases with excessive amounts of exogenous Hydrogen Peroxide on skin, may result in some systemic exposure. If Hydrogen Peroxide does penetrate the skin, it is presumed to degrade rapidly into molecular oxygen and water when in contact with blood or other body fluids; therefore, measurement of dermal penetration would not be possible. Despite the fact that Hydrogen Peroxide is a normal metabolite in cell metabolism and that Hydrogen Peroxide metabolism is understood (e.g., through catalase and glutathione peroxidase enzymes), data on the effects of exogenous Hydrogen Peroxide exposure in humans or animals are limited and mainly consist of case reports of oxygen embolization following the degradation of Hydrogen Peroxide after exposure to large amounts. No standard dermal penetration studies with Hydrogen Peroxide have been successfully conducted. Based on the physico-chemical properties of Hydrogen Peroxide, 100% dermal penetration should be used in the absence of more accurate information. ⁶

After application of 5 to 30% solutions of Hydrogen Peroxide on rat skin in vivo, some Hydrogen Peroxide could be localized in the excised epidermis within a few minutes. ¹¹ By contrast, with human cadaver skin in vitro, only after the application of high Hydrogen Peroxide concentrations for several hours, or after pretreatment with hydroxylamine (inhibitor of catalase), was Hydrogen Peroxide detectable in the dermis. Based on histochemical analysis, Hydrogen Peroxide was not metabolized in the epidermis, and the passage was transepidermal, avoiding the “preformed pathways” of skin appendages. The localization of dermal emphysema, caused by liberation of oxygen, correlated for the most part with the distribution of catalase activity within the tissue.

Absorption, Distribution, Metabolism, and Excretion (ADME)

Hydrogen Peroxide is a normal metabolite in aerobic cells. ¹¹ Hydrogen Peroxide passes readily across biological membranes. Under normal, physiological conditions, the concentration of Hydrogen Peroxide in tissues is 1 to 100 nM (0.034 to 3.4 μg/L) depending upon the organ, cell type, oxygen pressure, and cell metabolic activity. ³³

In biological systems, Hydrogen Peroxide is metabolized by catalase and glutathione peroxidases. ³³ The highest activities are found in highly vascularized tissues such as the duodenum, liver, kidney, and mucous membrane. ³⁴ In the metabolism of Hydrogen Peroxide to water and oxygen, the decomposition rate in human plasma is approximately 0.01 to 0.05 M/min. Catalase is more efficient at the decomposition of higher concentrations of Hydrogen Peroxide; glutathione peroxidase is more efficient at decomposing lower Hydrogen Peroxide concentrations. ³⁵ Glutathione peroxidase is present in cytosol and mitochondria but not in peroxisomes. A high glutathione peroxidase reduction activity of Hydrogen Peroxide is found in liver and erythrocytes; moderate levels are found in the heart and lungs, and a low activity is present in muscle.

In the presence of transition metals in cells, Hydrogen Peroxide can be reduced via the Haber-Weiss reaction. ³⁶ This reaction produces hydroxyl radicals (free radicals) which are highly reactive and can result in lipid peroxidation.

At high uptake rates, Hydrogen Peroxide can pass the absorption surface and enter the adjacent tissues and blood vessels, where it is rapidly degraded by catalases and molecular oxygen is liberated.^11,33 Consequently, mechanical pressure injury and oxygen embolism may be produced. In the view of the high degradation capacity for Hydrogen Peroxide in blood, it is unlikely that it is systemically distributed; therefore, the endogenous steady state levels of the substance in tissues are unlikely to be affected.

In rat blood diluted 1000 times, the half-life of Hydrogen Peroxide was less than 5 min at both 5 and 10 mg/L. ⁶ For 20 mg/mL, the half-life was more than 4 h. In the study, concentrations of Hydrogen Peroxide were much greater than the range of aqueous solutions in products or in-use concentrations. The study demonstrates the high efficacy of the antioxidative system in blood. Furthermore, it supports the view that if Hydrogen Peroxide is entering blood circulation, it is rapidly decomposed in blood and will not be systemically available. For this reason, the distribution of Hydrogen Peroxide in the body is expected to be very limited after exposure to Hydrogen Peroxide solutions. Due to the rapid endogenous transformation into water and oxygen, there is no specific excretion of Hydrogen Peroxide or a determinable degradation product. ³³

Acute Dose Toxicity

Acute dose toxicity studies in animals summarized below are presented in Table 6.

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Table 6.

Acute Toxicity Studies.

Animal (n)	Concentration	Dose/Concentration	Procedure	Results	Reference
Dermal
Mice (strain and n not specified)	10% and 28% aq.	1400 and 8000 mg/kg	Not specified	Clinical signs: excitation and inhibition, ataxia, tremors and paresis of the limbs, and increased respiration rate developed 5 to 10 min after dermal application at 1400 mg/kg. Death of some mice was observed on application of 28% Hydrogen Peroxide in doses >8000 mg/kg	11
White rats (12)	90% aq.	4899 and 5520 mg/kg	No details provided	Four of 12 died in the low-dose group and 9 of 12 died in the high-dose group	33
Black rats (6)	Not specified	6900 and 8280 mg/kg	No details provided	None of the rats died in the low-dose group and 2 of 6 rats died in the high-dose group	33
Rats (strain and n not specified)	Not specified	4060 mg/kg	No details provided	50% of the rats died	33
New Zealand White rabbits (10/sex)	35% w/w aq.	2000 mg/kg	OECD GL 402 (Acute Dermal Toxicity)Under occlusion for 24 h. Rabbits were observed at 0.5, 1, 2, 3, 4 and 6 h, twice daily for 13 days, and once on day 14 The rabbits were then killed and necropsied.	There were no deaths. Nasal discharge in one rabbit and lacrimation in another rabbit were observed on day 4 and 5, respectively. Seven rabbits gained weight and three rabbits lost weight. No gross lesions were observed at necropsy.LD50 > 2000 mg/kg	2,33
Male rabbits (4)	70% aq. w/w	6500 and 13,000 mg/kg	OECD GL 402	None of the rabbits died in the low-dose group; all rabbits in the high-dose group died.LD50 = 9200 mg/kg	2,33
Rabbits (12)	90% aq.	690 mg/kg	No details provided	Six of 12 rabbits died.	33
Cats (2)	90% aq.	4361 mg/kg	No details provided	None of the cats died	33
Pigs (5)	Not specified	2760 mg/kg	No details provided	Two of 5 pigs died	33
Oral
Mice (strain and n not specified)	90% aq.	Not specified	No detail provided	LD50 = 2000 mg/kg	33
Wistar rats (10/sex)	9.6% aq.	Males: 847 to 2529 mg/kgFemales: 886 to 2646 mg/kg	Gavage	All deaths occurred within 24 h. Surviving rats recovered within 4 to 24 h. Dose-dependent inhibition of autonomic behavior was observed immediately after dosing. At 3801.6 mg/kg or higher in males and 3974.4 mg/kg or higher in females, rats remained in a strongly inhibited state until their deaths, which occurred within 1 to 3 h. Necropsy of the rats that died showed a dose-dependent dilation of capillaries of the stomach and intestines starting at the lowest doses. No changes were observed in other organs.Males: LD50 = 1520 mg/kgFemales: LD50 = 1620 mg/kg	2
Wistar-JCL rats	9.6% aq.	Oral administration not specified	7-day observation period.	Males: LD50 = 1571 mg/kgFemales: LD50 = 1671 mg/kg	33
Sprague-Dawley rats (5/sex)	10% aq.	5000 mg/kg	OECD GL 401 (Acute Oral Toxicity)Rats were observed at 0.5, 1, 2, 3, 4 and 6 h, twice daily for 13 days, and once on day 14 The rats were then killed and necropsied.	No deaths occurred after dosing. One female rat died at day one after dosing, but no other mortality occurred during the observation period. Clinical signs included decreased locomotion, ataxia, and nasal discharge. Necropsy showed hemorrhagic, blood filled stomachs and intestines and reddened lungs.LD50 > 5000 mg/kg	2
Sprague-Dawley rats (10/sex)	35% w/w aq.	Males: 630, 794, 1000, 1260, 1588, and 2000 mg/kgFemales: 794, 1000, 1260, and 1588 mg/kg	Administered by gavage.Rats were observed at 0.5, 1, 2, 3, 4 and 6 h, twice daily for 13 days, and once on day 14 The rats were then killed and necropsied.	Mortality was observed at all doses; none survived in the 2000 mg/kg group. Most deaths occurred within 24 h of dosing. Clinical signs included tremors, decreased motility, prostration, and oral, ocular, and nasal discharge. Necropsy of rats found dead revealed hemorrhagic stomachs and intestines filled with blood. Reddened lungs and white tongues were observed. Less frequently, blood-filled bladders and stomach and livers containing white foci were observed. All surviving rats appeared normal at necropsy.Males: LD50 = 1193 mg/kgFemales: LD50 = 1270 mg/kg	2,33
Sprague-Dawley rats (n not specified)	50% aq.	Not specified	Observed for 14 days.	LD50 > 225 and <1200 mg/kgNo deaths among female rats, 1 of 5 male rat died on day one	11
Wistar rats (n not specified)	60% aq.	Males: 0, 0.351, 0.535, 0.734, 1.019 or 1.296 mL/kgFemales: 0, 0.213, 0.323, 0.426, 0.659, 0.879, 1.236 or 1.647 mL/kg	Observed for 14 days.	Males: LD50 = 872 mg/kgFemales: LD50 = 801 mg/kg	11
Crl:CD BR rats (5/sex)	70% w/w aq.	Males: 500, 1000 and 1500 mg/kgFemales: 500, 750 and 1000 mg/kg	OECD GL 401Observed for 14 days.	Two males in the 1000 mg/kg group, 1 female in the 500 mg/kg group, and 2 females in the 750 mg/kg group died. All males in 1500 mg/kg group and females in 1000 mg/kg group died; most were found dead on day of administration. Compound-related gross changes of the tongue, esophagus, stomach, and duodenum and adhesions in the peritoneal cavity were observed in male and female rats that died. Degenerative ulceration and regenerative hyperplasia of pyloric antrum of the stomach were observed at all dose levels. Ulcerative necrosis penetrated into the gastric epithelium (muscularis mucosa); severity of the ulcerations was rated minimal to mild.Males: LD50 = 1026 mg/kg (no confidence interval available)Females: LD50 = 693.7 mg/kg (95% confidence interval 427–960 mg/kg)Combined: LD50 = 805 mg/kg (no confidence interval available)	2
Rats (strain and n not specified)	70% aq.	50, 75 or 100 mg/kg	No details provided	Males: LD50 = 75 mg/kg	11
Dogs (6 treatment, 1 control)	3% aq.	2 mL/kg (not more than 45 mL)Control was administered apomorphine in the conjunctival sac.	Oral administration (method not specified) was repeated 10 min later if emesis had not occurred.	Emesis was successfully induced in 5 out of 6 dogs after one dose and on second dose with remaining dog. Mean time to emesis was 4.5 min and 2 min for apomorphine.Most severe lesions identified were gastric ulcers and gastric degeneration and necrosis, evident at 4 and 24 h following treatment. Most gastroduodenal lesions were present for up to 1 week, with resolution by 2 weeks. Duodenum was less affected grossly than esophagus or stomach, and was less affected than stomach histologically. Esophagus was not evaluated histologically.	37
Inhalation
Male Swiss mice (4)	70% w/w aq.	300, 616, 1135 and 1856 mg/m3	Nose-only exposure for a single 30 min period. Respiratory movements were recorded before, during and after exposure. After exposure, mice were observed for clinical signs and body weight changes up to 1 day after exposure. Mice were killed and gross pathology examinations were conducted, including a histopathological study of livers.	No mice died during the exposure. Respiratory RD50 was 665 mg/m3 (95% CI: 280–1139 mg/m3) and the exposure concentration at which a 50% reduction of the minute volume was observed was 696 mg/m3 (95% CI: 360–1137 mg/m3). Two mice in the 616 mg/m3 group and all mice in high-dose group had swollen white spots on the tip of the nose between 1 to 4 h after exposure. No other signs were observed. Two mice in 300 and 1856 mg/m3 groups (one each) had local degenerative changes of the liver.	2
Male OF1 mice (8)	Not specified	25, 39, 103, or 212 ppm (calculated as 35, 54, 143, or 295 mg/m3)	Head-only exposure for 60 min. Respiration was measured during exposure and recovery.	The onset of decrease in respiration started almost immediately at all concentrations and was steady through treatment period. Recovery was rapid, starting at 15 min, with respiration returning to 74% to 98% of pre-exposure.RD50 = 113 ppm (calculated as 157 mg/m3)	38
Mice (strain not specified; 10)	Not specified	3600 to 19,000 mg/m3	Exposed for 5, 10 or 15 min. Average mass median droplet size was approximately 3.5 μm.	There were no deaths up to 5000 mg/m3. Reported mortalities: 9462 mg/m3 for 5 min, no mortality; 13,287 mg/m3 for 10 min, 5 of 10 died; 11,877 mg/m3 for 15 min, 5 of 10 died; 16,809 mg/m3, 9 of 10 died.Exposures up to 5000 mg/m3 for 5 min caused nasal irritation, blinking, and slight gasping. At necropsy, lung congestion was observed. Four of 20 mice in the 5200 mg/m3 had necrosis of bronchial epithelium. At 9400 mg/m3 and higher for 5 to 15 min, mice had more severe signs and 10% to 15% of mice died within 1 h after convulsions. Necropsy showed pulmonary congestion. Mice that survived for several days to 8 weeks had necrosis of bronchial epithelium. Mice surviving 9400 mg/m3 or more had slowly developing corneal damage, which appeared 5 weeks after exposure.	33
Mice (strain and n not specified)	70% aq.	920 to 2000 mg/m3 and 12,000 to 13,000 mg/m3	2 h full-body exposure	Half of the mice died after 10 to 15 min of exposure at 12,000 to 13,000 mg/m3 Hydrogen Peroxide aerosol. Exposures at 920 to 2000 mg/m3 were lethal to at least some mice. Macroscopic examination of dead mice showed swelling and/or discoloration of skin of head, tongue, neck, forepaws, and nose; subcutaneous emphysema and hemorrhages; red lymph nodes; and diffuse red lungs. Effects were attributed to bleaching and corrosive nature of test substance.	11
Swiss-Webster Mice (4)	70% aq.	880 to 4960 mg/m3	7.5 to 120 min to aerosolized test material in nose-only apparatus. Surviving mice were observed for 14 days before necropsy.	No treatment-related mortalities were observed up to 3220 mg/m3 for up to 30 min. Longer exposure to 3130 mg/m3 (1 h) and 880 mg/m3 (2 h) was lethal. Clinical signs (not specified) were almost immediate. Time to recovery increased with time of exposure and concentration, but did not exceed 1 week. Effects at necropsy were attributed to bleaching or corrosiveness of test material. No changes in lung weights were observed. Macroscopic examination of surviving mice at end of recovery period showed no effects except bald area between eyes, suggesting that no permanent damage was caused by exposure to test material.	33
Swiss mice (10)	90% aq.	16.1 ppm (23 mg/m3)	4 h exposure followed by 2 weeks observation.	There were no mortalities.Lethal dose >16.1 ppm	39
Male mice (strain not specified; 4)	90% aq.	3600 to 19,000 mg/m3	Exposed for 5 to 15 min	At concentrations from 3600 to 5200 mg/m3, there were no deaths, but congestion of lungs and necrosis of bronchial epithelium were observed. At 9400 mg/m3, lethal range was reached with death occurring 6 days following exposure. At 12,000 to 19,000 mg/m3 for 10 to 15 min, survival time was reduced in majority of mice to less than 1 hClinical signs during exposure to low concentrations consisted of mild nasal irritation, blinking eyes, slight gasping, and loss of muscular coordination, which resolved within 30 min. Pulmonary congestion was noted, and surviving mice had necrosis of bronchial epithelium.LCLO = 9400 mg/m3	2
Sprague-Dawley rats (5/sex)	50% aq. w/w	170 mg/m3 (122 ppm)	US EPA Guideline Vol 50 (§798.1150) (Acute Inhalation Toxicity)Atmosphere was generated by bubbling air flow through a reservoir containing 1000 mL of 50% aq. Full body exposure for 4 h followed by observation for 14 days. Rats were then killed and necropsied.	Signs of treatment were minimal during exposure (decreased activity and eye closure) but a few responses such as nasal discharge were noted during 14-day observation period. A minimal, transient adverse effect upon body weight was produced by treatment. Otherwise, body weight gain was considered unremarkable. At necropsy, observations and lung weights were considered unremarkable. No LD50 value for acute inhalation toxicity could be established and must be greater than the maximum attainable vapor concentration of 170 mg/m3.	2,33
Male Wistar rats (18)	90% aq.	Not specified	Rats were exposed to vapor in glass chamber for 8 h. Rats were killed and necropsied periodically over next 14 days.	No rats died and there were no clinical signs observed. Only abnormal signs noted were rats scratching and licking themselves. Pathological examination showed congestion in trachea and lungs. Small, localized areas of pulmonary edema without hemorrhage and areas of alveolar emphysema were present among rats killed during first 3 days after exposure. Most lungs exhibited many areas of alveolar emphysema in addition to severe congestion. All other organs examined appeared normal.	40
Male Wistar rats (10, 20)	90% aq.	338 to 427 mg/m3	Rats were exposed to vapor in glass chamber for 4 h (n = 10) or 2 8-h (n = 20) exposures.	There were no deaths reported from either single 4-h exposure or two 8-h exposures. Only abnormal signs noted were rats scratching and licking themselves. Pathological examination showed congestion in trachea and lungs. Small, localized areas of pulmonary edema without hemorrhage and areas of alveolar emphysema were present among rats killed during first 3 days after exposure. Most lungs exhibited many areas of alveolar emphysema in addition to severe congestion. All other organs examined appeared normal.	40
Male Wistar rats (5)	90% aq.	16.1 ppm (23 mg/m3)	4 h exposure followed by 2 weeks observation.	There were no mortalitiesLethal dose >16.1 ppm (22.52 mg/m3)	39
Sprague-Dawley rats (4, 6, 13)	Not specified	0, 0.01, 0.02, 0.1 ppm (calculated as 0, 0.014, 0.025, or 0.14 mg/m3)	Rats were exposed for 2h in a nose-only apparatus. Rats were killed and lungs were examined immediately (n = 4 or 6) or 24 h (n = 4 or 13) after exposure.	There were no changes observed in light microscopy at 0.014 and 0.025 mg/m3; electron microscopy revealed an increase in number of neutrophils in capillary spaces adjacent to terminal respiratory bronchioles and in alveolar ducts in lungs from rats after inhalation of 0.025 mg/m3 (not observed at 0.14 mg/m3). There were no changes in cell number, cell viability, and BAL fluid LDH at any concentration or time period when compared to controls. There was an increase in serum LDH only at 0.025 mg/m3 at 24 h. There was an increase in TNF-α at both time periods and reactive oxygen intermediates (superoxide anion) at 24 h. Nitric oxide production was decreased at all concentrations.The authors suggest that vapor-phase Hydrogen Peroxide reaches the lower lung and modulates macrophage function.	41
Rats (strain not specified; 3)	Not specified	Not specified	4 h exposure	Threshold concentration of Hydrogen Peroxide vapors for increase of NAD-diaphorase in rat bronchial epithelium was 60 mg/m3. Threshold for skin effects (moderate hyperemia and transient thickening because of oxygen bubbles in skin) was 110 mg/m3. Authors concluded that primary cause of death was gas embolus.LC50 = 2000 (1690–2360) mg/m3LOEC for respiratory mucosa = 60 mg/m3LOEC for skin effects = 110 mg/m3	2
Male and female New Zealand White rabbits (8)	Not specified	0.75, 7.5, or 37 mg/m3 in saline (total inhaled dose = 0, 0.1, 1.4, 7.1 mg, respectively)Controls exposed to aerosolized saline.	4 h using a nebulizer	Exposure to Hydrogen Peroxide aerosols did not alter baseline airway resistance, dynamic elastance, slope of inspiratory pressure generation, or arterial blood pressure and blood gas measurements.	42

Short-Term Toxicity Studies

Oral

Short-term oral toxicity studies summarized below are presented in Table 7.

OPEN IN VIEWER

Table 7.

Oral Repeated Dose Studies of Hydrogen Peroxide.

Animal (n)	Concentration of Hydrogen Peroxide	Dose or Drinking Water Concentration	Duration	Methods/Procedure	Results	Reference
Short-Term Toxicity Studies
Male dd mice (n not specified)	Not specified	0.3%, 0.6%, or >1%	2 weeks	Administered in drinking water	There was a decrease in body weight gains in 0.6% group but not 0.3% group. There was a decrease in body weight gains and death within 2 weeks at >1%.	33
C57BL/6NCrlBR mice (10/sex)	Not specified	0, 200, 1000, 3000, or 6000 mg/L (w/v)	14 days	Administered in drinking water	No toxic signs were observed in 0 to 3000 mg/L groups. Water consumption was reduced in a dose-dependent manner in the 1000 mg/L and greater groups. Body weight gains were reduced in the 3000 and 6000 mg/L group first 3 days, which was thought to be due to dehydration. Decreased body weights and feed consumption were observed in high-dose group throughout study. Gross pathological examination was unremarkable. Histopathology showed degenerative (minimal to mild erosions) and regenerative (minimal to mild) hyperplasia changes in mucosa of the stomach and/or duodenum in the 3000 and 6000 mg/L groups in both sexes.Overall NOAEL for pathology was 1000 mg/L for both sexes (males = 164 mg/kg, females = 198 mg/kg)	33
Male Osborne-Mendel rats (n not specified)	Not specified	0 or 0.45%	3 weeks	Administered in drinking water	There was a decreased intake of liquid, which was reflected in total body weight of treated rats (average weight 108 g) compared to controls (156 g). Control rats consumed tap water at an average of 544 mL/day, whereas the treated rats consumed an average of 282 mL/day. There were no differences in relative weights in testes, kidneys, spleen, or heart.	45
Male Osborne-Mendel rats (n not specified; 3)	Not specified	0 or 0.45%	3 weeks	Administered in drinking water; control group was limited to the amount of water consumed by the test group.Older rats with an average weight of 600 g were administered Hydrogen Peroxide in drinking water for 3 weeks and weighed. they were then administered tap water for 3 weeks and weighted	Rats in control group continued to seek water after their allotment was consumed; the test group did not. Average body weight for the test group was 116 g vs. 104 g in the control group. There were no differences in relative or dry weights in testes, kidneys, spleen, or heart.Weight decreased to an average of 511 g. The rats regained the lost weight by the end of 3 weeks on tap water.	45
Wistar rats (n = 10/sex)	Not specified	0, 0.6, 1, 2, 3, or 6 mg/100g bw (0, 6, 10, 20,30 or 60 mg/kg/d)	40 days	Administered by oral catheter. Controls received water.	No deaths were reported.No toxic effects were observed at doses <30 mg/kg/day. Body weight decreased (5%) at and after 20 days of administration in high-dose group. At highest dose, hematocrit values and blood plasma protein concentrations were lower; in 30 and 60 mg/kg groups, plasma catalase activity was lower.Gross pathology: There were slightly higher spleen weights at 40 days. (60 mg/kg/day).LOAEL = 30 mg/kg/day	46
Rats (n not specified)	Not specified	1/5 and 1/10 LD50 (actual dose not specified)	45 days	Gavage	Both doses caused decreased body weight gain, increased blood peroxidase activity, decreased liver catalase activity, increased circulating reticulocytes, and increased urinary albumin. Stomach walls showed inflammatory responses at both doses with severity in a dose-dependent manner.	33
Holtzman rats (24)	Not specified	0, 0.5%, 1.0%, and 1.5%	8 weeks	In drinking water	Mortality: 7 of 24 in the high-dose group died. Dose-dependent extensive carious lesions and pathological changes in the periodontium. Body weight gain was reduced in a concentration-dependent manner in all treatment groups.	47
Male Wistar JCL rats (n not specified)	5% aq.	56.2, 168.7, or 506.0 mg/kg	12 weeks	6 days/week by gavage	High-dose group had reduced body weight gain and reduced hemoglobin concentration, erythrocyte count, blood corpuscle volume, serum SGOT, SGPT, and alkaline phosphatase activity. Mid-dose group had abnormalities in kidney function. Kidney, liver, and heart weights were decreased and adrenal and testes weights were increased in the high-dose group. Erosion and scars of gastric mucosa was observed in high-dose group.	3,33
Subchronic Toxicity Studies
C57BL/6NCrlBR mice (n = 15/sex)	35% w/w aq. Hydrogen Peroxide added to water	0, 100, 300, 1000, or 3000 ppm	∼90 days	OECD GL 408 (Repeated Dose 90-Day Oral Toxicity in Rodents) Administered in drinking water. After dosing period, 10 mice/group were killed and necropsied and remainder were allowed a 6-week recovery period. This strain of mice was chosen due to particular sensitivity to Hydrogen Peroxide because of a deficient detoxification pathway and, therefore, be regarded as a very sensitive animal model for this particular substance.	No treatment-related deaths occurred and no treatment-related clinical signs were observed at any time. Male and females exhibited significant reductions in body weight at 3000 ppm. Feed and water consumption were reduced in the 3000 ppm group but not in 1000 and 300 ppm groups. Males in the 3000 ppm group displayed reductions in total protein and globulin levels in blood, possibly caused by mucosal hyperplasia occurring in their duodenums. Necropsy revealed no treatment-related gross lesions. Microscopic examination showed an increase in cross-sectional diameter and wall thickness of the duodenum. Subsequent microscopic evaluations revealed mild mucosal hyperplasia in 8 of 9 males in 3000 ppm group and in 7 of 10 males in the 1000 ppm group. Minimal mucosal hyperplasia was observed in 1 of 10 males in 300 ppm group. Minimal to mild mucosal hyperplasia was also observed in 10 of 10 females in 3000 ppm group and in 8 of 10 females in 1000 ppm group. No other areas of the gastrointestinal tract were affected. No evidence of cellular atypia or architectural disruptions or any other indications of neoplastic changes were observed; therefore, treatment-related mucosal hyperplasia noted was not considered as a neoplastic lesion.Based on dose-related reductions in feed and water consumption and observation of duodenal mucosal hyperplasia, LOEL = 300 ppm and NOEL = 100 ppm (26 and 37 mg/kg/day for males and females). Clinical pathologic effects (decreased total protein and globulin blood levels) were limited to 3000 ppm level. All effects noted during treatment period were reversible; mice necropsied following recovery period were considered biologically normal.	2
Male Wistar rats (n = 10/sex)	Not specified	0, 0.6, 1, 2, 3, or 6 mg/100g (0, 6, 10, 20, 30 or 60 mg/kg)	100 days	Administered in feed.	No deaths were reported.There were no significant effects to body weights, organ weights, or blood chemistry observed at all doses	46
Chronic Toxicity Studies
C57BL/6J mice (50/sex)	Not specified	∼300 or 1200 mg/kg/day; 0.1% or 0.4%	100 weeks	In drinking water	Erosion and ulcers in the glandular stomach and hyperplasia, adenomas and carcinomas in the duodenum were observed. Erosion in the stomach occurred after 40 weeks. No metastases or other treatment-related tumors were observed. Body weights were significantly reduced in the high dose females after 15 months.	49,50
Male and female rabbits (n not specified)	Not specified	0.005, 0.05, 0.5, 5, or 50 mg/kg/day; 0.00001%, 0.0001%, 0.001%, 0.01%, or 0.1%	6 Months	Administered by gavage daily	High-dose group had decreased body weights and blood lymphocyte concentrations; increased numbers of reticulocytes and hemolysis, albuminuria; decreased hepatic catalase activity, increase hepatic succinyl-dehydrogenase activity, changes in enzyme activity of stomach, duodenum, cerebrum; structural changes of gastrointestinal mucosa; and focal fatty changes in hepatocytes.Low-dose groups only had changes in hematology and enzyme activities.NOAEL = 0.005 mg/kg/day [Study appears to not be included in DFG safety evaluation due to insufficient documentation.]	2,113

DFG = Deutsche Forschungsgemeinschaft; LOAEL = lowest observed adverse effects level; LOEL = lowest observed effects level; NOEL = no observed effects level; NOAEL = no observed adverse effects level; SGOT = serum glutamic oxaloacetic transaminase; SGPT = serum glutamic pyruvic transaminase.

In general, orally administered Hydrogen Peroxide caused inflammation of and erosion to the upper digestive tract of mice and rats. Mice administered Hydrogen Peroxide (0.3 and 0.6%) in drinking water had decreased body weights over 2 weeks; mice died when administered 1% Hydrogen Peroxide or greater. ³³ In another 2-week study in mice exposed to Hydrogen Peroxide in drinking water, the mice had reduced water consumption and weight gains at 1000 mg/L and greater; at necropsy, degenerative (minimal to mild erosions) and regenerative (minimal to mild hyperplasia) changes in the mucosa of the stomach and/or duodenum in the 3000 and 6000 mg/L groups in both sexes were observed. ³³ The overall NOAEL for pathology was 1000 mg/L for both sexes.

In a 3-week drinking water study in rats of 0.45% Hydrogen Peroxide, there was a decrease in fluid consumption and body weights; there were no differences in relative weights in testes, kidneys, spleen, or heart. ⁴⁵ In a 40-day oral study in rats, no deaths were reported and no toxic effects were observed at doses <30 mg/kg/day (via gavage), but blood effects (reduction of hematocrit values, blood plasma proteins concentrations, and plasma catalase activity) were observed at 60 mg/kg; the lowest-observed-adverse-effects-level (LOAEL) was 30 mg/kg/day. ⁴⁶ In another gavage study in rats, administration of 1/5 and 1/10 of the LD₅₀ (actual dose not specified) for 45 days caused blood effects (increased blood peroxidase activity) and inflammatory responses in the stomach wall. ³³ In an 8-week drinking water study, 7 of 24 rats died in the 1.5% Hydrogen Peroxide group; dose-dependent extensive carious lesions and pathological changes in the periodontium were observed. ⁴⁷ In a 12-week oral gavage toxicity study in rats, there were no mortalities at up to 506 mg/kg of 5% aq. Hydrogen Peroxide, but there were blood effects (reduced hemoglobin concentration, erythrocyte count, blood corpuscle volume, serum glutamic-oxaloacetic transaminase (SGOT), and serum glutamic pyruvic transaminase (SGPT)) at this dose; there were also changes to the weights of kidneys, livers, and hearts (decreased) and to adrenal glands and testes (increased).^3,33

Inhalation

Short-term inhalation toxicity studies summarized below are presented in Table 8.

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Table 8.

Inhalation Repeated Dose Studies of Hydrogen Peroxide.

Animal (n)	Concentration of Hydrogen Peroxide	Air Concentration	Duration	Methods/Procedure	Results			Reference
Short-Term Toxicity Studies
Mice (10)	90%	79 or 107 mg/m3	up to 4 weeks	79 mg/m3: 6 h/day for 2 to 3 days/week (8 exposures) or 107 mg/m3: 6 h/day; 3 days/week during week 1; 5 days/week for weeks 2–4 (18 exposures)		After week 2: both groups had nasal discharge, edematous feet, irritation of skin in the groin regionAfter week 5: both groups had hair loss around the nose, probably due to scratching due to irritation7 of 9 mice died after 8 exposures in the low-dose group; 5 of 10 mice died after 8 exposures in the high-dose group, 8 of 10 mice died after 18 exposures.LOAEL = 79 mg/m3		40
Alpk:ApfSD Wistar rats (n = 5/sex)	50% aq.	2.88, 14.6, 33.0 mg/m382.4 mg/m3 then 38.7 mg/m3	28 days	OECD GL 412 (Subacute Inhalation Toxicity: 28-Day Study)Whole body chambers for 5 days per week, 6 h per day.A fourth group of rats was exposed to 82.4 mg/m3) on days 1, 4, 5 and 6. Exposure level was reduced to 38.7 mg/m3 on days 11 and 12. Treatment was terminated on day 13 and rats were euthanized due to toxicity.		Clinical signs were observed in rats exposed to 14.6 mg/m3 and greater. In general, number and severity of these clinical signs increased with repeated exposure at low doses, whereas the onset of clinical signs was earlier at higher doses but also a certain degree of recovery from symptoms was seen at higher doses. Clinical signs included reddened nose, stains around snout and mouth, salivation, signs of respiratory tract irritation, irregular breathing, urinary incontinence, piloerection, chromodacryorrhea, hunched posture, increased response to touch, and thin appearance. Some evidence of recovery was observed after treatment ended.Body weights gradually decreased in males in 33.0 mg/m3 group and in males and females in 82.4/38.7 mg/m3 group. Feed consumption was reduced in males in 33.0 mg/m3 group and in males and females in 82.4/38.7 mg/m3 group. Minor effects on hematology in 33.0 mg/m3group, which were not considered biologically and toxicologically significant. In both sexes, there was a minimal decrease in albumin and total protein levels in 33.0 mg/m3group. Kidney weights increased in females in 33.0 mg/m3 group. Relative lung weights in males and relative kidney weights in females in 33.0 mg/m3 group were increased. Treatment-related findings were observed in nasal and oral cavities of rats at necropsy at end of study. Staining of nares was observed at 14.6 mg/m3 and above and mouth staining was at 33.0 mg/m3; in both cases, no dose-response could be found. Increased findings, including necrosis, inflammation and perivascular neutrophil infiltration, in exposed rats over controls during the microscopic examinations were observed in the nasal cavity, larynx, and lung.Clinical observations were consistent with test material being a respiratory tract irritant (reddened noses, stains around nose, and abnormal respiratory noise); in general, time to onset, incidence and severity of clinical signs increased with exposure concentration and repeated exposure. Males exposed to 33.0 mg/m3had lower feed consumption and body weight gain compared to controls. Minimal changes in albumin and total protein blood levels were observed in males and females in 33.0 mg/m3 group. Histopathological, treatment-related changes were observed in anterior-most regions of nasal cavity lined with squamous epithelium, where minimal to slight necrosis (with associated inflammation) and rhinitis were observed in rats in 10.3 and 33.0 mg/m3 groups. Inflammation and epithelial erosion in larynx and increased perivascular neutrophil infiltration in lungs were considered unlikely to be related to treatment due to absence of a clear dose response relationship. NOEL was 2.9 mg/m3 and LOAEL was 14.6 mg/m³.		2
Rats (strain not specified; 23; 10 for mortality studies and 13 for pathology)	90%	0 or 93 mg/m3	7 weeks	6 h/day, 2 or 3 days/week for weeks, 1 and 2, respectively, 5 days/week during weeks 3–7, for 30 exposures1–2 pathology group rats were killed each week for necropsy		There were signs of nasal irritation and profuse nasal discharge after 2 weeks exposure. Lung congestion (primarily slight congestion) was observed in all rats killed throughout study, and tracheal congestion was observed at weeks 5 and 7. Hair loss around the nose, probably due to scratching due to irritation, was observed after week 5. One rat died. No significant microscopic changes were observed at necropsy.		40
Black rabbits (Strain not specified; 8)	90%	30 mg/m3 (22 ppm) vapor	12 weeks	6 h/day, 5 days/week. Whole body exposure.		No effects were observed except for bleaching of fur and some nasal irritation.		40
Subchronic Toxicity Studies
Rats (strain and n not specified)	Not specified	0.1, 1.0, or 10.1 mg/m3	Up to 4 months	5 h per day, 5 day per week for up to 4 months for whole body exposures. Some of the mice were shaved for dermal exposure [See Subchronic Toxicity Studies for dermal results]		Threshold concentration for lung effects was 10 mg/m3. At 2 and 3 months in 10 mg/m3 group, there was an increase in serum epoxidase activity (2.50 and 2.63, respectively; controls, 2.16 and 2.20, respectively). After 4 months lungs showed a decrease of SDH (0.26 versus 0.34 in controls). Studies of lungs showed a decrease in activities of SDH, MAO, acid phosphatase, diesterase, and an increase in activity of alkaline phosphatase.NOEL = 1 mg/m3LOEL = 10 mg/m3	2,33
Wistar rats (n = 10/sex)	50% aq.	1.5, 3.6, 10.3 mg/m3	13 weeks	OECD GL 413 (Subchronic Inhalation Toxicity: 90-Day Study)Nose-only apparatus for 6 h per day, 5 days per week		There were no mortalities during study. No treatment-related clinical abnormalities or ocular changes were observed. No significant treatment-related effects were observed for body weight gains or feed consumption. At necropsy, no treatment-related effects were observed on any hematology or white blood cell parameters tested. Of clinical chemistry parameters tested, there was an increase in alkaline phosphatase concentrations in male rats in high-concentration group, which was not considered an adverse effect when compared to historical control data. Liver and thymus weights (both absolute and relative to body weight) of male rats in high-concentration group were decreased. However, this weight change was not accompanied by microscopic abnormalities in these organs and values were consistent with historical control data. No effects were observed on weights of any of other organs or tissues of rats (male or female). No treatment-related effects were observed at microscopic examination of any organ or tissue, including respiratory tract.NOAEL = 10.3 mg/m3 for male and female rats.	2
Rabbits (n and strain not specified)	90% aq.	22 ppm (calculated as 30.77 mg/m3)	3 months	Daily; no other details provided		Irritation was noted around nose	29
Chronic Toxicity Studies
Dogs (2)	90%	10 mg/m3	26 weeks	6 h/day, 4 to 5 days/week		At 14 weeks, there were no effects observed except for fur bleaching and loss. After 23 weeks, sporadic sneezing and lacrimation were observed. There were no weight changes or changes in clinical chemistry and hematology. Lungs had areas of atelectasis and emphysema and there were some hyperplasia in bronchial musculature.	40

LOAEL = lowest observed adverse effect level; MAO = monoamine oxidase; NOAEL = no observed adverse effects level; NOEL = no observed effects level; OECD = Organisation for Economic Co-operation and Development; SDH = succinate dehydrogenase activity.

Mice exposed to Hydrogen Peroxide (90% aq.; 79 or 107 mg/m³) for 6 h per day for 2 to 3 day per week, for up to 4 weeks, had nasal discharge, edematous feet, and irritation of the skin at week 2 and hair loss around the nose (probably due to scratching due to irritation) at week 5; seven of nine mice died after eight exposures in the low-dose group, and in the high dose group, five of 10 mice died after eight exposures and eight of 10 died after 18 exposures. ⁴⁰ Rats exposed to aerosolized Hydrogen Peroxide (50% aq.) 5 days per week, 6 h per day, for 28 days showed clinical signs at 14.6 mg/m³ (including reddened nose, salivation, irregular breathing), but not at 2.88 mg/m³; the no-observed-effects-level (NOEL) was 2.9 mg/m³ and the LOAEL was 14.6 mg/m³. ² Rats exposed to 93 mg/m³ Hydrogen Peroxide (90% aq.) for 6 h per day for 2 to 5 days per week for 7 weeks (30 exposures) showed signs of nasal irritation and profuse discharge at 2 weeks, lung congestion and hair loss (probably due to scratching due to irritation) at 5 weeks. ⁴⁰ In black rabbits exposed to 90% Hydrogen Peroxide (30 mg/m³) vapor for 6 h per day, 5 days per week for 12 weeks, there were no effects observed except for the bleaching of the fur and some irritation around the nose. ⁴⁰

Subchronic Toxicity Studies

Chronic Toxicity Studies

Dermal

The teratogenicity of nine oxidative hair dye formulations was tested using Charles River CD rats (n = 20). ⁴⁸ The oxidative formulations were each mixed 1:1 with Hydrogen Peroxide (6% aq.) immediately prior to application (2 mL/kg/day) to shaved backs. The test materials were applied to the shaved dorsoscapular area of pregnant rats on every third gestation day (GD days 1, 4, 7, 10, 13, 16, and 19). Positive controls were administered oral acetylsalicylic acid (250 mg/kg) on GD 6 to 16. Three separate negative control groups were shaved, but not treated. No maternal toxicity was observed, there were no treatment effects on implantation or intrauterine growth, or survival, and there was no evidence of external, visceral, or skeletal malformation.

Six composite test materials, representative of commercial oxidative hair dye formulations, were evaluated in Sprague-Dawley rats (n = 20/sex) in a two-generation study of reproduction. ⁵¹ The dyes were each mixed 1:1 with Hydrogen Peroxide (6% aq.) and then applied (0.5 mL) twice weekly to the clipped backs of the rats. The treatment of the F₀ rats began at 6 to 8 weeks of age, and rats of the second litter (F_1b) began treatment at weaning. Breeding for both generations began at 100 days of age, and dermal applications continued throughout mating, gestation, and lactation periods. Occasional mild dermatitis was the only adverse effect noted. Body weight gain, feed consumption, survival, and reproductive indices (fertility, gestation, live birth and survival, and weaning weight) in F_1a, F_1b, F_2a, and F_2b litters were similar to controls.

Oral

Hydrogen Peroxide (30% aq.; 0.33% and 1%) was administered to male mice (strain and n not specified) in drinking water for 7, 21, or 28 days premating.^2,4 After mating, the female mice were also administered Hydrogen Peroxide (0, 0.33% or 1%) in drinking water. All mated female mice became pregnant, the pups were healthy, and the litters were of normal size. Pregnant mice in the high-dose group had some delay in parturition compared to controls; however, the effect was small and inconsistent. The concentration, morphology, and motility of the spermatozoa (tested in three mice) after 3 weeks of treatment appeared normal.

Female and male Osborne-Mendel rats (n not specified) were administered Hydrogen Peroxide (0.45%) in drinking water for 5 months prior to mating. ⁴⁵ The females continued to be treated through parturition. Six of the male offspring were also administered Hydrogen Peroxide (0.45%) in drinking water for 9 months. The litters of the treated females were normal. The only observed effect in the male offspring was a statistically significant reduction in weight (411 g vs 521 g in controls).

Aqueous solutions of Hydrogen Peroxide (0.02%, 0.1%, 2%, or 10%) were mixed with powdered feed and administered to pregnant Wistar rats (n = 7 to 11) for 1 week “during the critical period of pregnancy” (no further explanation was provided; no control group was specified). ¹¹ Most of the dams (n = 5 to 8) were killed and the pups removed and examined on gestation day 20; some (n = 2 to 3) were allowed to deliver their pup and were followed for 4 weeks. The body weights of the dams in the high-dose group did not increase markedly. Fetal resorptions were increased and the fetal body weights were decreased. Most of the fetuses were close to death. No external malformations were observed in any group. Hemorrhaging (in the eyes, parietal region of the brain, cardiopulmonary region, and torso) increased dose-dependently in the 0.1% to 10% dose range. Skeletal hypoplasia was dose-dependent in the two highest dose groups. In the litters that were allowed to be delivered, all of the neonates in the high-dose group died within 1 week post-partum. Body weights were low and the number of live births decreased in the high-dose group. In the other groups there was no major effect on the development of neonates.

It was reported that the concentration of Hydrogen Peroxide in the feed decreased to 1/10 after 24 h and to almost zero at 72 h. The authors of the study stated that “the amount of residue was determined and consumption was estimated;” however, it is not stated how frequently fresh feed was prepared. Nevertheless, it seems likely that the dams did ingested Hydrogen Peroxide, evidenced by that there was not much of an increase in dam body weight at the high-dose level. The authors proposed that the observed effects on fetal development were due to the breakdown of essential nutrients in food by Hydrogen Peroxide.

Male and female rats (strain and n not specified) were administered Hydrogen Peroxide (0.005 to 50 mg/kg; 1/10 to 1/5 LD₅₀; vehicle not specified) by gavage for 6 months. ⁵² Females had modified estrus cycles and the males had decreased sperm mobility. The rats were then mated. At the highest dose, 3 out of 9 females produced litters, compared to 7 out of 9 in the control group (not described). Body weights of the offspring in the high-dose group were reduced compared to controls.

In Vitro

There are numerous genotoxicity studies of Hydrogen Peroxide. A representative sample is presented here. When available, the starting concentration of the Hydrogen Peroxide tested is stated in Table 9.

The results in Ames assays conducted on Hydrogen Peroxide were not consistent. In most of the Ames assays presented, Hydrogen Peroxide (concentrations not specified in most assays) increased the number of revertant colonies in Salmonella typhimurium strains without metabolic activation (3% or 30% in those assays with concentrations of Hydrogen Peroxide provided)^53-58; however, there were a few assays where the results were negative for genotoxicity (3% in two of these assays).^33,56,58-60 In one assay with metabolic activation, 3% Hydrogen Peroxide was mutagenic in strain TA100, but not in TA98, TA1535, TA1537, and TA1538, ⁵⁸ and in another, Hydrogen Peroxide (concentrations not specified) without metabolic activation was weakly mutagenic in strain TA102, but less genotoxic with metabolic activation.^33,59 In Ames assays in Escherichia coli, Hydrogen Peroxide was positive for genotoxicity in one assay (concentrations not specified), ⁶¹ and negative for genotoxicity in another assay (3% Hydrogen Peroxide). ⁵⁸ Results were ambiguous for S. typhimurium TA100 up to 7.5 μmol/plate ⁶² and positive for TA102 at 75 μg/plate without metabolic activation. ⁶¹ In one other assay, Hydrogen Peroxide was genotoxic to E. coli without metabolic activation and not mutagenic with metabolic activation. ⁶³ In other Ames-type assays, Hydrogen Peroxide (concentrations not specified) was mutagenic in E. coli, Bacillus subtilis, and Saccharomyces cerevisiae.^64-66

In bacterial forward mutation assays, Hydrogen Peroxide (30% aq.) was genotoxic to E. coli K12 kat(−) and kat(+) strains at 75 and 600 nmol/ml, respectively, ⁶⁷ and to E. coli (DB2) starting at 24 μg/ml (concentrations not specified). ⁶⁸ Hydrogen Peroxide was genotoxic to B. subtilis (168DB) at 0.0005% aq. ⁶⁵ Hydrogen Peroxide (concentration not specified) was not genotoxic to Chinese hamster lung fibroblast (V79) cells up to 300 μmol. ⁶⁹ In an l-arabinose bacterial forward mutation assay, Hydrogen Peroxide (concentrations not specified) was genotoxic to S. typhimurium (BA9 and BA13) starting at 2941 nmol/ml. ⁷⁰

In a chromosomal aberration test, Hydrogen Peroxide (concentration not specified) was genotoxic to Chinese hamster ovary (CHO) cells starting at 10 nL/mL with metabolic activation and 25.31 nL/mL without metabolic activation, ² and in a second test, Hydrogen Peroxide (30% in saline) was genotoxic to Chinese hamster fibroblasts at 0.25 mg/plate. ⁷¹ Hydrogen Peroxide (concentration not specified) was also mutagenic to murine splenocytes, ⁷² V79 cells,^69,73 and Syrian hamster embryo (SHE) cells^69,74 in chromosomal aberration tests. Hydrogen Peroxide (concentration not specified) was mutagenic to human leukocytes and embryonic fibroblasts.^33,75 Hydrogen Peroxide increased the number of abnormal metaphases in CHO-K1 cells without, but not with, metabolic activation. ⁶⁹

In mouse lymphoma assays, Hydrogen Peroxide increased the mutation frequency in mouse lymphoma cells without metabolic activation.^2,76 Hydrogen Peroxide did not increase the mutation frequency in mouse lymphoma cells with metabolic activation.

In various assays, Hydrogen Peroxide had mixed results in V79 cells.^69,77-80 In sister chromatid exchange (SCE) assays, Hydrogen Peroxide (concentrations not specified) was mutagenic in V79 cells without metabolic activation, but was not mutagenic, or was mutagenic to a lesser extent, with metabolic activation.^73,78,81,82 Hydrogen Peroxide (concentrations not specified) was mutagenic in CHO cells starting at 10 to 20 μM without metabolic activation, but was not mutagenic, or was mutagenic to a lesser extent, with metabolic activation.^78,83-87 Hydrogen Peroxide (concentrations not specified) increased the number of SCEs at 300 μM in SHE cells. ⁸⁸ Hydrogen Peroxide (concentrations not specified) was mutagenic at 20 μM in human lymphocytes but not in whole blood; metabolic activation reduced Hydrogen Peroxide-induced SCEs. ⁸⁴ Hydrogen Peroxide (concentrations not specified), without metabolic activation, was mutagenic to D98/AH2 human cells. ⁸⁹

In an endo-reduplicated cells assay, Hydrogen Peroxide (concentrations not specified) was mutagenic to CHO AUXB1 cells starting at 160 μM in a dose-dependent manner. ⁸⁵ In an unscheduled DNA synthesis (UDS) in mammalian cells assay using rat hepatocytes, Hydrogen Peroxide (35.7% aq.) caused a dose-dependent increase in net nuclear grain (NNG) values at 6.25 to 25 μg/ml. ²

In comet assays, Hydrogen Peroxide was genotoxic in mouse lymphoma cells, ⁹⁰ rat hepatocytes, ⁹¹ S. cerevisiae, ⁹² and V79 cells (40 μM; 37% aq.). ⁹³ Hydrogen Peroxide was also mutagenic to human breast adenocarcinoma cell lines MCF-7 and MCF-10A, ⁹⁴ human lymphocytes, ^93,95 human fibroblasts (30 μM; 37% aq.),^93,96 immortalized cervical cancer (HeLa) cells (30 μM),^93,97 and liver hepatocellular carcinoma (HEP G2) cells (40 μM; .3 M).^93,98 In a combined comet assay/micronucleus assay using human lymphoblastoid TK6 cells, Hydrogen Peroxide (concentration not specified) was genotoxic in the comet assay at 50 μM and at 100 μM in the micronucleus assay. ⁹⁹ In another combined comet assay/micronucleus assay in V79 cells, Hydrogen Peroxide was genotoxic at 80 μM and at 40 μM, respectively. ¹⁰⁰

In a multi-test assay, Hydrogen Peroxide (concentration not specified) was not genotoxic in two DNA adduct assays up to 500 μM (but was genotoxic at 500 μM in a comet assay), at 20 μM in a micronucleus test, and at 100 μM in a tk+/− gene mutation assay, all using L5178Y tk+/− mouse lymphoma cells. ⁹⁰ Hydrogen Peroxide (37% aq.) was not mutagenic at 110 μM in V79 cells in a hypoxanthine-guanine phosphoribosyltransferase (HPRT) assay. ⁹⁶

In Vivo

Animal

Human

IARC determined that there is inadequate evidence in humans to come to a conclusion on the carcinogenicity of Hydrogen Peroxide and that there is limited evidence in experimental animals on the carcinogenicity of Hydrogen Peroxide. ¹⁰⁷ IARC concluded that Hydrogen Peroxide “is not classifiable as to its carcinogenicity to humans (Group 3).”

Co-Carcinogenicity

Dermatitis and Alopecia

Hair dye ingredients, including Hydrogen Peroxide (concentration not specified), were applied to the dorsal region of female C57BL/6 mice (n = 5 or 6) daily for 3 consecutive days and evaluated for dermatitis and hair loss. ¹¹¹ The test materials were applied to the backs of the mice (2 × 5 cm) for 30 min; the test sites were then washed with tap water. The applied concentrations were selected based on their respective contents in commercial hair dye products. Three days after final hair-dyeing, photographs of mice were taken and the extent of hair loss was determined by measuring the area without hair using image processing and analysis software. Signs of hair loss and dermatitis (epidermal hyperplasia and inflammatory cell infiltration in the deep dermis and subcutaneous fat layer) developed in all groups treated with the component combinations containing Hydrogen Peroxide and the neutralized dye mixture (containing monoethanolamine (MEA) and toluene-2,5-diamine sulfate/p-phenylenediamine/resorcinol). The groups without either Hydrogen Peroxide or the neutralized dye mixture did not have hair loss or dermatitis, suggesting that both Hydrogen Peroxide and the neutralized dye mixture were necessary for inducing hair loss and dermatitis.

The experiment was repeated with the following test materials: (a) control (treated with a basic formulation of hair dye); (b) 6% MEA +10% neutralized dye mixture; (c) 4.5% aq. Hydrogen Peroxide; and (d) 6% aq. Hydrogen Peroxide +4.5% MEA +10% neutralized dye mixture. The group that contained Hydrogen Peroxide and MEA had increased hair loss compared to controls. Hydrogen Peroxide or MEA alone or in other combinations did not increase hair loss.

In a third experiment, Hydrogen Peroxide (6% aq.) was administered to the mice with MEA (0%, 3%, or 6%) and MEA (6%) was administered to the mice with Hydrogen Peroxide (0%, 3%, or 6% aq.). There was no hair loss or dermal damage when Hydrogen Peroxide or MEA were administered alone. There was a concentration-dependent increase in hair loss and dermal damage for Hydrogen Peroxide with the addition of MEA and for MEA with the addition of Hydrogen Peroxide. The authors concluded that hair dye-induced hair loss and dermatitis were caused by the combination of Hydrogen Peroxide and MEA. ¹¹¹

Irritation

Animal

Dermal irritation studies in animals are summarized in Table 11.

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Table 11.

Dermal Irritation Studies of Hydrogen Peroxide in Animals.

Animal (n)	Concentration	Procedure	Results	Reference
New Zealand White rabbits (6)	3% aq. (volume not specified)	Administered to intact and abraded skin under occlusion for 24 h.	PII = .125 out of 8Not irritating	2
Rabbits (not specified)	3% aq. (volume not specified)	24 h exposure under occlusion. Observation at 24 and 72 h.	PII = 0 at both observations. Non-irritant	33
Albino rabbits (6)	6% aq. (89% water, 5% not specified; 0.5 mL)	Administered to intact and abraded skin under occlusion for 24 h.	Erythema and edema were observed at 24 and 72 h.PII at 24 h = 0.75 out of 8PII at 48 h = 0.70.Classified as not irritating.	2
Rabbits (not specified)	6% aq. (volume not specified)	24 h exposure under occlusion. Observation at 24 and 72 h.	PII = 0 at both observations. Non-irritant	33
Rabbits (6)	8% aq. (0.5 mL)	Administered to intact and abraded skin under occlusion for 24 h.	Erythema and edema were observed at 24 and 72 h after administration.PII = 0.04 out of 8.	2
Rabbits (not specified)	8% aq. (volume not specified)	24 h exposure under occlusion. Observation at 24 and 72 h.	PII = 0 at both observations. Non-irritant	33
New Zealand White rabbits (3/sex)	10% aq. (0.5 mL)	OECD GL 404 (Acute Irritation and Corrosion)Under semi-occlusion to shaved skin for 4 h. Rabbits were observed at 30 min and 24, 48, and 72 h after removal.	Slight erythema was observed in 2 rabbits up to 24 h post-dosing, which was resolved at 48 h.PII = 0.08 out of 8Not irritating.	2
Rabbits (not specified)	10% aq. (volume not specified)	24 h exposure. Observation at 4.5, 24, 48, and 72 h. (further details not provided)	PII = 0.3, 0.2, 0, and 0 out of 8 at 4.5, 24, 48, and 72 h, respectively. Non-irritant	33
New Zealand White rabbits (3/sex)	35% aq. (0.5 mL)	Under occlusion to shaved skin for 4 h. Rabbits were observed at removal and daily for 2 weeks.	Scores for erythema/eschar were not higher than 2 for individual rabbits at any time. Mean scores were 1, 1.75, 0.58 and 0.58 out of 8 at 4, 24, 48 and 72 h. Scores for edema were not higher than two for individual rabbits at any time. Mean scores were 1.83, 0.83, 0 and 0 at 4, 24, 48 and 72 h. After 14 days, 2 rabbits had brown areas with desquamation at the test sites. Test material was judged to be moderately irritating to the rabbit’s skin and was non-corrosive within 48 h of dosing.PII = 1.6 out of 8	2
Rabbits (not specified)	35% aq. (volume not specified)	4 h exposure to intact skin under occlusion. Observed at 4, 24, 48, 72, and 96 h.	PII = 2.8, 2.6, 0.58, 0.58, and 0.42 out of 8 at 4, 24, 48, 72, and 96 h, respectively. Non-irritant	33
New Zealand White rabbits (10/sex)	35% w/w aq. (2000 mg/kg; volume not specified)	OECD GL 402 (Acute Dermal Toxicity)Under occlusion for 24 h. Observed at 0.5, 1, 2, 3, 4 and 6 h, twice daily for 13 days, and once on day 14. Rabbits were then killed and necropsied.	Erythema, edema, and blanching of the test sites were observed in all rabbits 24 h after administration. By day 4, all rabbits had necrosis which developed into eschar on day 7. At termination of the study, eschar and exfoliation were present in all rabbits.	2
Rabbits (6)	35% w/w aq. (volume not specified)	Administered for 24 h (further details not provided)	Mild erythema with moderate to slight edema in all 6 rabbits at 24 h, and severe to moderate erythema with slight to very slight edema in all 6 rabbits at 48 h.Irritating	2
Female New Zealand White rabbits (1)	49.2 % aq. (0.5 mL)	OECD GL 404Rabbit was anesthetized prior to dosing. Under semi-occlusion to 2 sites for 4 h then observed at 30 min and 24 and 48 h.	Severe erythema, moderate edema, and gray areas were observed on both test sites at 24 h. Moderate erythema, slight edema, gray areas, and ataxia were present at 48 h. Histopathologic examination showed severe irritation that would have resulted in ulceration and necrosis.PII = 5 out of 8	2
Rabbit (1)	50% or 70% aq.	Draize AssayExposure of 70% for 3 min and 50% for 3 min and 1 and 4 h.	Exposure to 50% Hydrogen Peroxide for 3 min caused moderate erythema and mild edema. Mild erythema and no to mild edema were observed at 24, 48, and 72 h after treatment. No dermal irritation was observed at 7 or 14 days. Blanching was observed at time of dosing in test site of rabbit treated with 70% Hydrogen Peroxide. After 3 min, mild erythema and severe edema were observed around area of blanching. Moderate or mild erythema and moderate or mild edema were observed at 24, 48, and 72 h. Sloughing and fissuring were also observed. Superficial necrosis was observed at 24, 48, and 72 h after treatment; necrosis was observed at 7 days. Scar tissue was observed at 14 days.Exposure to 50% Hydrogen Peroxide for 1 h produced slight erythema, severe edema, and blanching. Mild erythema with mild, slight or no edema was observed through day 7 of observation. No erythema or edema was observed on day 14 after treatment. Superficial necrosis was observed in test site at 72 h after treatment, and necrosis and sloughing were observed at 7 days. Scar tissue was observed at 14 days.Exposure to 50% Hydrogen Peroxide for 4 h produced mild erythema, moderate edema, and blanching by end of exposure period. Blanching was observed through 48 h. Moderate, mild, or slight erythema and mild, slight, or no edema was observed through day 7 after treatment. No erythema or edema was observed at day 14. Superficial necrosis was observed at 72 h and necrosis and sloughing were observed at day 7. Scar tissue and sloughing were observed at day 14.70% Hydrogen Peroxide, 3 min exposure was corrosive50% Hydrogen Peroxide, 1 or 4 h exposure was corrosive	2
Male rabbits (4)	70% w/w aq. (6500 and 13,000 mg/kg; volume not specified)	OECD GL 402 (further details not provided)	Observation of the skin revealed redness, massive edema, eschar formation, and sloughing off at application sites.	2
Rabbit (1)	70% aq. (volume not specified)	OECD GL 404Exposure for 1 h (further details not provided)	Test site had slight erythema, severe edema and white bubbles under the skin. At 24 h there was still mild erythema, edema, and white bubbles under the skin accompanied by several 1 to 2-mm brown spots. At 48 h, findings were similar but brown spots had enlarged to spotted areas. Corresponding Draize scores at 30 min and 24 and 48 h were 0.4, 0.3, and 0.3 out of 8, respectively. Histopathological lesions were consistent with those occurring in third degree burns. Test material was judged to have caused extensive damage to dermis, epidermis, blood vessels, connective tissue, and adnexa.Corrosive	2
Mice (strain and n not specified)	15% or 30% aq.	Single application to the dorsal skin	Extensive epidermolysis, inflammation and vascular injury, similar to that produced by tumor promoters, followed by quick regeneration and epidermal hyperplasia, with a temporary increase in number of dark basal keratinocytes. Extensive endothelial damage to dermal blood vessels also occurred.	105
Wistar WBN/Kob-Ht rats (5)	0, 3%, 6%, or 10% aq.; 0.04 mL	Each concentration was administered to 1 of 4 sites on the shaved dorsal skin for 7 consecutive days. Another group of untreated rats acted as additional controls.Rats were killed and skin examined 1 day after last application.	Skin exposed to 3% Hydrogen Peroxide had mild focal epidermal thickening, which had keratinocytes with signs of pyknosis. Intracytoplasmic edema was sporadically observed at and around thickened skin, especially in basal layer. Mild infiltration of mononuclear cells was sporadically observed in the superficial dermis. Deeper dermis layers had an increase in number of mast cells.At 6%, changes observed at 3% progressed and border between the epidermis and dermis became irregular. There were portions where epidermis was partially detached from dermis, leaving a space filled with fluid.At 10%, focal trans-epidermal necrosis was observed in some sites. Skin lesions were observed.At all concentrations, necrotic keratinocytes were observed scattered in spinous and basal layers, and necrotic keratinocytes were occasionally ingested by macrophages. Basal layer contained clusters of keratinocytes with signs of shrinking cell bodies and/or intracytoplasmic edema and occasional infiltration of basement membrane. Marked degenerative changes were detected occasionally in capillary endothelial cells in superficial dermis.	112
Guinea pigs (not specified)	9 solutions of Hydrogen Peroxide at 3% and 6% aq. (volume not specified)	Administered to intact and abraded skin (further details not provided).	None of 9 solutions was more than mildly irritating when applied to intact skin (initial patch reactions). When applied to abraded skin, 2 of 9 solutions (one at 3% and one at 6%) were strongly irritating, while other preparations were at most only mildly irritating.	2

OECD GL = Organisation of Economic Co-operation and Development Guide Lines; PII = primary irritation index.

In rabbits, generally, Hydrogen Peroxide was not irritating at up to 10% aq. and mildly irritating to irritating at 35% aq.; at approximately 50% aq. and above, Hydrogen Peroxide was severely irritating and corrosive.^2,33 Hydrogen Peroxide was not irritating to intact and abraded skin at 3% and 6% aq. in rabbits.^2,33 At 8% and 10% aq., erythema and edema were observed, but Hydrogen Peroxide was still rated as a non-irritant.^2,33 At 35% aq. Hydrogen Peroxide, erythema, edema, and blanching of the test sites were observed in rabbits, and the test substance was found to be a dermal irritant.^2,33 At 49.2% aq., Hydrogen Peroxide was corrosive to rabbit skin. ² Dermal exposure to 50% aq. Hydrogen Peroxide for 1 or 4 h exposure was corrosive. ² Dermal exposure to Hydrogen Peroxide at 70% aq. for 3 min caused moderate erythema and mild edema, and exposure for 30 min was corrosive. ³³

A single application of 15% or 30% aq. Hydrogen Peroxide caused extensive epidermolysis, inflammation and vascular injury to mouse skin. ¹⁰⁵ In rats, skin exposed to 3% to 10% aq. Hydrogen Peroxide had mild focal epidermal thickening, which had keratinocytes with signs of pyknosis. ¹¹² Intracytoplasmic edema was sporadically observed at and around thickened skin, especially in the basal layer. The severity of the effects increased in a dose-dependent manner. Different solutions of 3% or 6% Hydrogen Peroxide were non-irritating or mildly irritating to intact guinea pig skin; in abraded skin, one of these solutions at 3% and one at 6% were strongly irritating, while the other preparations were at most only mildly irritating. ²

Sensitization

In Vitro

A 21-day porcine corneal opacity reversibility assay (PorCORA) was conducted on a hair colorant mixed 1:1 with Hydrogen Peroxide (12% aq.). ¹¹⁵ Ocular irritation effects were observed (microscopic changes only in the superficial squamous cell layer), but were fully reversible.

Animal

Ocular irritation studies in animals are summarized in Table 12.

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Table 12.

Ocular Irritation Studies for Hydrogen Peroxide.

Animal (n)	Concentration	Method/Assay	Results	Reference
Rabbits (strain and n not specified)	0.5% aq. (drop)	Dropped onto cornea of eye	Caused disturbances of epithelium, but eyes returned to normal within 24 h	116
Albino rabbits (6)	3% aq. (.1 mL)	Test substance was instilled once and not washed out. Eyes were examined with a bright artificial light and hand-slit lamp at 24, 48, and 72 h after treatment.	No irritant response was observed within 72 h after instillation.	2
Female New Zealand White rabbits (4)	5% aq. (0.1 mL)	OECD GL 405 (Acute Eye Irritation/Corrosion)0.5 % Tetracaine Hydrochloride was used to minimize pain.Eyes of 2 of 4 rabbits were washed 20 to 30 sec after instillation and scored after 1, 24, 48, and 72 h.	1 h after instillation, all treated eyes had slight conjunctivitis. At 24 h, slight to mild conjunctival redness was noted in all treated eyes. Three treated eyes had slight redness 48 h after instillation. At 72 h, all irritation was resolved.Slightly irritating	2
Rabbits (strain and n not specified)	5% aq. (0.1 mL)	Eyes of some rabbits were washed 20 to 30 sec after instillation and scored after 1, 24, 48, and 72 h.	Draize score: a Unwashed: 8.0, 3.0, 2.0, and 0 and washed: 6.0, 3.0, 1.0, and 0 at 1, 24, 48, and 72 h, respectively.Irritation scores: b C = 0; I = 0; R = 0.83; H = 0.Non-irritant	33
New Zealand White rabbits (6)	6% aq. (0.1 mL)	OECD GL 405Eyes of 3 rabbits were unwashed; eyes of 3 rabbits were washed for 1 min with water 20 sec after instillation.Eyes were examined at 1, 24, 48, and 72 h after instillation; 2 rabbits of each treatment group were examined after 7 days and 1 was examined 14 and 21 days following treatment.	Slight to severe irritating effects in both unwashed and washed eyes were observed, which were reversible in most cases within 72 h following treatment. Treated eye in 1 rabbit was normal after 7 days. Moderate to severe corneal damage was observed in 1 rabbit. Corneal vascularization, which may be interpreted as a sign of healing, was still present in this rabbit after 21 days.Serious eye irritant	2
Rabbits (strain and n not specified)	6% aq. (0.1 mL)	Eyes of some rabbits were washed 20 to 30 sec after instillation and scored after 1, 24, 48, and 72 h and 14 and 21 days.	Draize score: a unwashed at 1, 24, 48, and 72 h and 7 days: 19.0, 5.2, 3.3, 0.7, and 0, respectively, and at 1, 24, 48, and 72 h washed: 27.0, 15.0, 19.7, and 5 respectively; <4 and <7 for 1 rabbit evaluated at 14 and 21 days, respectively.Irritation scores: b Unwashed: C = 0; I = 0; R = 1.33; H = 0.2 and washed: C = 0.4; I = 0.22; R = 1.33; H = 0.78.Non-irritant.	33
Male New Zealand White rabbits (4)	8% aq. (0.1 mL)	OECD GL 4050.5 % Tetracaine hydrochloride was used to minimize pain.Treated eyes of 2 rabbits remained unwashed, while the eyes of the 2 remaining rabbits were washed 20 to 30 sec following instillation. Eyes were examined at 1, 24, 48, and 72 h and days 4, 7, 10, 13, 16, 19, and 22.	Moderate conjunctivitis was observed in all eyes1 h after dosing. Irritation worsened by 24 h at which time unwashed eyes had slight corneal opacities, iritis, and severe conjunctivitis. Washed eyes had severe corneal opacities, severe iritis and conjunctivitis. Irritation gradually resolved in unwashed eyes; washed eyes developed corneal vascularization on day 7 and bulging of the cornea (1 rabbit) on day 13. At day 22, 1 unwashed eye had a slight corneal opacity and eye of the remaining rabbit in the group with washed eyes had a slight corneal opacity, mild conjunctivitis and vascularization. Washing eyes with tap water shortly after exposure increased severity of irritation observed.One rabbit of the group with washed eyes died on Day 21 of the study due to enteritis (possibly stress-related) and was not considered to be directly related to treatment.Ocular irritant	2
Rabbits (strain and n not specified)	8% aq. (0.1 mL)	Eyes of some rabbits were washed 20 to 30 sec after instillation and scored after 1, 24, 48, 72, and 96 h and 7, 16, and 21 days.	Draize score: a Unwashed: 13.0, 31.0, 11.0, 5.0, 4.0, 2.0, 2.5, and 2.5; washed: 12.0, 84.5, 77.5, 71.0, 57.0, 47.0, 22.0, and 16.0 at 1, 24, 48, 72, and 96 h and 7, 16, and 21 days, respectively.Irritation scores: b C = 1.66; I = 0.50; R = 2.50; H = 1.58.Irritant	33
Female New Zealand White rabbits (4)	10% aq. (0.1 mL)	OECD GL 405Treated eyes of 2 rabbits remained unwashed, while eyes of 2 remaining rabbits were washed 20 to 30 sec following instillation. Eyes were examined up to 7 days after instillation.	1 h after instillation, moderate to severe conjunctivitis was observed in all eyes; 1 washed eye had a hemorrhagic conjunctiva. Within 24 h, severe corneal opacities, iritis, and conjunctivitis were observed in all eyes. Three rabbits had conjunctival hemorrhages. Eyes gradually improved until day 7, at which time corneal opacities were present in all eyes; iritis was observed in 1 unwashed and 1 washed eye, and conjunctivitis was observed in all treated eyes. Washing eyes with tap water shortly after exposure increased severity of irritation observed.Irritation scores at 24 and 72 h: Cornea opacity = 4 and 2.75; Iris = 2 and 1; conjunctivae = 3 and 3, respectively.Extremely irritating	2
Rabbits (strain and n not specified)	10% aq. (0.1 mL)	Eyes of some rabbits were washed 20 to 30 sec after instillation and scored after 1, 24, 48, 72, and 96 h and 7 days.	Draize score: a Unwashed: 11.0, 107, 107, 71.0, 44.5, and 40.5; washed: 15.0, 108, 108, 81.0, 65.5, and 49.0 at 1, 24, 48, 72, and 96 h and 7 days, respectively.Irritation scores: b C = 3.5; I = 1.67; R = 3.0; H = 2.8.Irritant	33
Male New Zealand albino rabbits (12)	10% and 15% aq.	Applied directly to cornea of right eye of each rabbit. Macroscopic assessments for irritation were made 3 h, and 1, 3, and 35 days after dosing. Light microscopic examinations were conducted. In vivo confocal microscopy and measurements of dead corneal epithelial cells and keratocytes at 3 h and 1 day were used to characterize quantitatively initial corneal injury. In vivo confocal microscopy performed at 3 h and 1, 3, 7, 14, and 35 days was used to characterize corneal changes over time.	Changes with 10% and 15% Hydrogen Peroxide were consistent with severe irritation. Both concentrations affected the epithelium and deep stroma. High concentration also, at times, affected endothelium. However, there was an incongruity between extent of epithelial and stromal injury, with stromal injury being more extensive than epithelial injury.	117
Rabbits (strain and n not specified)	35% aq. (0.1 mL)	Eyes of some rabbits were washed 20 to 30 sec after instillation and scored after 1, 24, 48, 72, and 96 h and 7, 14, and 22 days.	Draize score:a Unwashed: 39.2, 62.5, 69.5, 69.5, 63.7, 79.3, 74.8, and 72.7; washed: 41.3, 49.0, 69.7, 59.7, 48.7, 76.7, 76.0, and 74.3 at 1, 24, 48, 72, and 96 h and 7, 14, and 22 days, respectively.Irritation scores: b C = 2.33; I = 1.72; R = 1.27; H = 2.28.Irritant	33
Female New Zealand White rabbits (8)	70% aq. (0.1 mL)	Draize testThe rabbits were observed for 72 h after dosing.	There was extreme irritation with maximum corneal, iridial, and conjunctival effects. One rabbit died 10 min after instillation. Draize score was not determined.Corrosive; risk of serious damage to eyes	2,33
Black rabbits (Strain not specified; 8)	30 mg/m3 (22 ppm) vapor; concentration not specified	6 h/day, 5 days/week. Whole body exposure for 12 week (60 exposures).	Ophthalmologic examination showed no changes due to exposure to test material.	40
Male mice (strain not specified; 4)	3.6–19 mg/L aerosolized; 90% aq.	Exposed for 5 to 15 min	Gross opacities were present in eyes of 4 mice exposed to 19 mg/L (highest concentration) at 8 weeks after exposure. Microscopic lesions were observed in eyes of mice exposed to 9.4 mg/L 8 weeks after exposure, while those necropsied at 5 weeks after exposure showed no significant changes. Authors concluded that these findings indicate that there is an insidious and slowly developing corneal damage subsequent to exposure to high aerosol concentrations of Hydrogen Peroxide.	2

In general, when rabbit eyes were treated with Hydrogen Peroxide, corneal injury depended not only on the concentration of Hydrogen Peroxide, but also on the integrity of the corneal epithelium, which had a protective influence. ¹¹⁶ Hydrogen Peroxide at 0.5% to 5% aq. instilled into the eyes caused superficial corneal haze and much conjunctival reaction in rabbits, but these effects were resolved in 24 hr.^2,116 Hydrogen Peroxide at 6% aq. had mixed results when instilled into the eyes of rabbits and was found to be both an ocular non-irritant and an irritant,^2,33 while at 8% aq., Hydrogen Peroxide was an ocular irritant.^2,33 Instillation of 10% to 30% aq. Hydrogen Peroxide caused superficial corneal haze, and, if there were defects in the epithelium, could cause localized swelling and opacities in the corneal stroma.^2,33 At 70% aq., Hydrogen Peroxide was corrosive to the rabbit eye.^2,33 In one study, Hydrogen Peroxide (10% and 15% aq.) was severely irritating; both concentrations affected the epithelium and deep stroma. ¹¹⁷

Rabbits exposed to 90% Hydrogen Peroxide vapor (30 mg/m³ for 6 hours day, 5 days/week) showed no ocular changes due to exposure to test material. ⁴⁰ Mice exposed to Hydrogen Peroxide (90% aq.) vapors (19 mg/L) for 5–15 minutes showed gross opacities and microscopic lesions in the eyes. ²

Human

Instilling 1% to 3% aq. Hydrogen Peroxide solution on the human eye has been reported to cause severe pain, which soon subsides. ¹¹⁶ In contrast, Hydrogen Peroxide has been historically used at these concentrations as an ocular antibacterial agent, as much as three to five times per day, without significant injury. While the threshold for irritation in many subjects is considered to be 100 ppm (0.01% aq.), even at 800 ppm (0.08% aq.), Hydrogen Peroxide has been shown to not cause corneal or conjunctival epithelial staining; higher levels may result in greater discomfort. It is possible that pH may play a role in the variation in irritation levels and why similar concentrations of Hydrogen Peroxide may cause severe pain or be tolerated.

Solutions (isotonic and pH-balanced for the human eye; 300 milliosmoles (mOsm), pH = 7) containing Hydrogen Peroxide (30 ppm to 490 ppm; 0.003% to 0.049% aq.) were dropped into one eye of each subject (n = 10; a single group of subjects) and a control dose containing Hydrogen Peroxide (30 ppm; 0.003%) was dropped into the other eye in a single blinded study. ¹¹⁸ The tests started with the lowest concentration (30 ppm). The subjects reported their comfort response at 1 and 10 min after the drops were administered. Subjects were asked to compare the discomfort in their eyes and to report if they felt stinging. If there was no stinging reported, the next concentration was administered at the next session. No more than two test sessions were run per day. The mean detection threshold for drops of dilute Hydrogen Peroxide was 812 ppm (0.0812% aq.). The intersubject variability was quite large. If the lowest reported threshold for any stimulus is considered as an individual’s threshold level for sensation, the mean value is 247 ppm (0.0247% aq.).

Animal

Hydrogen Peroxide (30% aq.; 5 μL) was dropped on the tip of the tongues of anesthetized male albino Osborne-Mendel rats (n = 18) four times at 15 min intervals. ¹¹⁹ The tongues were rinsed with water 15 min after the last application. Three to six rats were killed either right after rinsing or 1 or 7 days after the last application, and their tongues examined. Hydrogen Peroxide caused an almost immediate marked edema on the anterior part of the tongue. After 1 day, this edema turned into a large ulceration that healed almost completely after 7 days.

Hydrogen Peroxide (1% or 1.2% aq.) was administered to the gingiva or tongues of anesthetized dogs by continuous drip (time and volume not specified). ³³ Edema developed, followed by destruction and sloughing of the cornified epithelial layer of the gingiva.

Human

Repeated use of Hydrogen Peroxide topical solution as a mouthwash or gargle may produce a condition known as “hairy tongue” or may cause irritation of the buccal mucous membrane. ²⁹ Concentrated solutions (20% to 30% aq. or more) of Hydrogen Peroxide are strongly irritating to mucous membranes.

A mouth rinse containing Hydrogen Peroxide (concentration not specified) was tested in a double-blind, stratified, two-treatment, parallel trial (n = 48) over a 4-week period in cancer patients undergoing chemotherapy from two cancer treatment centers. ¹²⁰ Controls were administered baking soda and water rinses or a lemon glycerin solution. There were no adverse effects reported during this study. The original source document, published in 1999, does not provide the concentration of Hydrogen Peroxide in the mouth rinse.

Mucosal Irradiation

Syrian hamsters (n = 15) were used in an oral mucosal irritation assay to study the effects of Hydrogen Peroxide with irradiation. ¹²¹ The cheek pouches of the hamsters were treated as follows: group 1 was administered pure water (control); group 2 was administered laser irradiation at 80 mW; Group 3 was administered 3% aq. Hydrogen Peroxide; and groups 4 to 6 were administered 3% aq. Hydrogen Peroxide and laser irradiation at 80, 40, and 20 mW, respectively. The total treatment time was set at 7 min and treatment was repeated three times at approximately 1-h intervals. Macroscopic and microscopic histologic observations of the treated sites were performed immediately after each treatment and/or 24 h after the last treatment. The mean scores in macroscopic and histologic examinations in all six groups were 0. The authors concluded that treatment with 3% Hydrogen Peroxide and/or irradiation had no mucosal irritation potential in hamster cheek pouches under these test conditions.

Retrospective and Multicenter Studies

Clinical Trials

Other Clinical Studies

In patch tests using a standard hairdressers’ series in subjects (n = 54) who were hairdressers in Australia with occupational contact dermatitis of the skin and nails, none of the subjects had an allergic reaction to Hydrogen Peroxide (concentration tested not specified). ¹³⁰ In patch tests in subjects who were hairdressers (n = 164) in Australia with occupational contact dermatitis, none of the subjects had an allergic reaction to Hydrogen Peroxide (concentration tested not specified). ¹³¹ In patch tests in subjects who were hairdressers (n = 44) in Bangkok with contact dermatitis of the hands, three of the subjects had an allergic reaction to Hydrogen Peroxide (3% aq.). ¹³²

Case Reports

Case reports on dermal, oral, mucosal, ocular, and inhalation exposures to Hydrogen Peroxide are summarized in Table 13.

OPEN IN VIEWER

Table 13.

Case Reports on Exposure to Hydrogen Peroxide.

Dose, Concentration, and vehicle (if known)	Report	Reference
Dermal
3% aq. Hydrogen Peroxide in commercial hair dye	Two women had been exposed to Hydrogen Peroxide as an ingredient in commercial hair dyes. Both women tested positively to 3% Hydrogen Peroxide and numerous other ingredients in the hair dyes. The author reported that 156 other hairdresser patch tested with hairdresser series tested negatively to 3% Hydrogen Peroxide.	4
30% aq. Hydrogen Peroxide	A 31-year-old man presented with right knee pain after industrial-strength Hydrogen Peroxide (30%) splashed onto his pants while he was working in a leather factory. He denied any trauma. Physical examination showed 2% of total body surface area with second- to third-degree degree chemical burns with yellowish leathery skin covered with air-filled bullae and tenderness with subcutaneous crepitation over the right knee. He had a white cell count of 9200/mm3 with predominance of neutrophil (85.1%); radiography disclosed subcutaneous air around the right knee soft tissue. Under the diagnosis of chemical burn injury of the right knee, the patient received debridement and wound management.	138
Oral
Approximately 230 g of 3% aq. Hydrogen Peroxide solution (dose estimated at 600 mg/kg)	A 16-month-old boy died 10 hours after ingestion. On postmortem examination there was frothy blood in the right ventricle and in the portal venous system. The gastric mucosa was red and the brain was edematous. Histopathology showed edema in the lungs, diffuse interstitial emphysema and gas emboli within the pulmonary vasculature and gastrointestinal lymphatics. Clear vacuoles were also found within the spleen, kidneys and myocardium	139
3% aq. Hydrogen Peroxide2 to 4 oz	A previously healthy 3-year-old boy ingested 3% Hydrogen Peroxide. Approximately 30 min later, foam was noted in his mouth and he began to vomit. He experienced blood streaked emesis 15 min after drinking water. A radiograph of the abdomen for air embolization was negative. Upper GI endoscopy showed a normal esophagus, but there were multiple ulcers located in the gastric antrum, and multiple erosions were noted in the duodenal bulb. Repeat endoscopy 1 week later showed healing gastric and duodenal ulcers with no active bleeding or evidence of stricture formation.	140
A mouthful of 3% aq. Hydrogen Peroxide	A healthy 21-year-old male presented with vomiting and pain in his mouth, throat, and epigastrium. He was tachycardic and mildly hypertensive but not hypoxic. Clinical examination revealed dysphonia with mild erythema and edema of the oropharynx and uvula. CT scan showed pneumatosis and mucosal thickening throughout the stomach and proximal duodenum, as well as extensive portal venous gas. An upper endoscopy performed 3 days after the ingestion was normal, with no evidence of mucosal injury. A repeat CT scan showed interval partial resolution of the bowel wall thickening and complete resolution of the pneumatosis and portal venous gas.	141
3% aq. Hydrogen Peroxide (dose estimated at 40 mL)	A 25-year-old woman who had ingested Hydrogen Peroxide presented with epigastric pain and persistent vomiting with a small amount of blood. She had mild tenderness in the epigastric area. Numerous symptoms were found in the gastric tract including multiple large round mucosal erosions in the distal esophagus and diffuse hemorrhagic gastritis involving the entire gastric mucosa. Two days after admission, the hemoglobin concentration decreased and test result for occult blood in the stool was positive. The patient showed erythematous gastritis and resolution of the esophageal lesion on day 14.	142
One swallow of 30% aq. Hydrogen Peroxide	A 5-year-old presented with vomiting and epigastric pain. Radiographic evaluation showed portal venous gas embolism. Upper gastrointestinal endoscopy showed diffuse hemorrhagic gastritis. He was observed for 12 days and discharged. Follow-up endoscopy, 9 days later, showed erythematous gastritis.	143
Approximately 50 mL of 33% aq. Hydrogen Peroxide solution	Five persons who accidentally drank the solution experienced stomach and chest pain, retention of breath, foaming at the mouth and loss of consciousness. Later, they experienced motor and sensory disorders, fever, micro-hemorrhages and moderate leukocytosis. One subject developed pneumonia. All recovered completely within 2 to 3 weeks.	8
113 to 170 g of 35% aq. Hydrogen Peroxide (dose estimated at 3800 mg/kg)	A 2-year-old boy ingested the solution. He had gas in the heart and in the portal venous system, together with severe hemorrhagic gastritis without perforation. After death on day 4, autopsy showed marked diffused cerebral edema.	144
1 pint bottle of 35% aq. Hydrogen Peroxide	A 33-yr-old woman vomited, collapsed, and experienced a brief tonic-clonic seizure within minutes of ingestion. The patient was intermittently seizing and markedly cyanotic and had copious white foam emanating from her mouth. Within 30 sec after nasotracheal intubation, the patient became apneic and dependent on mechanical ventilation. She had mild erythema of the distal esophagus and diffuse hemorrhages and edema of the gastric mucosa. Bilateral cerebral hemisphere swelling was followed by patchy areas of weakness in the upper and lower extremities and truncal ataxia with inability to maintain a sitting position.	145
120 mL of 35% aq. solution Hydrogen Peroxide (dose estimated at 600 mg/kg)	A 63-year-old man who ingested the solution vomited three times and complained of general malaise. Laparotomy 5 h after ingestion showed severe erythema, edema, and emphysema of the gastric serosa; a visible perforation was not detected. Multiple brain embolisms were observed by MRI. On the fifth hospital day, the patient became alert and complained of numbness of the extremities. Neurologic examination demonstrated a left hemiparesis predominantly affecting the lower limb while sparing the face and a mild weakness of right lower limb. Abdominal symptoms rapidly improved, but recovery from the neurologic deficits was only partial.	146
30 mL of 35% aq. Hydrogen Peroxide (dose estimated at 150 mg/kg)	Ingestion of Hydrogen Peroxide resulted in brain injury presumed to be due to cerebral oxygen embolism in an 84-year-old man. Multiple cerebral infarctions (detected with MRI) occurring immediately after ingestion. Authors suggested that pathophysiologic mechanism was a patent foramen ovale of the heart (not said to be involved in the case), some unmetabolized Hydrogen Peroxide crossing the pulmonary capillary bed into the arterial circulation, or aspiration and absorption of Hydrogen Peroxide from the pulmonary capillaries.	147
Approximately 2 tablespoons of 35% aq. Hydrogen Peroxide	An elderly woman drank Hydrogen Peroxide and developed respiratory distress within a few min. She had a frothy mouth and soon became unresponsive. A CAT scan of the chest/abdomen/pelvis showed air in the heart, spleen, and splenic and portal veins. She exhibited an altered mental status. She was treated with phenytoin, midazolam for seizure prophylaxis and hyperbaric oxygen for the air embolism without improvement.	148
Mucosal
3% aq. Hydrogen Peroxide	A 35-year-old man presented with severe pain and erythema of the lower labial mucosa. He had self-medicated for halitosis and gingivitis by applying 3% Hydrogen Peroxide to the region with a cotton swab. A few hours later, he experienced painful oral ulcerations at the site of application. There was an extensive area of ulceration and erythema involving the alveolar mucosa and the marginal and attached gingival region. Focal areas of ulceration and sloughing with necrosis of surface layers of the epithelium were also observed. The patient discontinued use of Hydrogen Peroxide, and the area was gently rinsed with saline to remove necrotic tissue. The 1-week follow-up examination showed complete healing.	149
Ocular
3% aq. Hydrogen Peroxide disinfectant solution	A woman who had inadvertently stored a contact lens in a 3% Hydrogen Peroxide disinfectant solution had an immediate painful reaction with hyperemia, tearing, and eyelid spasm. Her eye became increasingly inflamed over the next 48 h (despite anti-inflammatory drops), the cornea began to show punctate staining, and the conjunctiva was edematous. Her cornea began to clear after 48 h and the pain reduced. Visual acuity had dropped to 20/40 and recovered to 20/20. Several days later, there seemed to be no residual effects, except minimal punctate keratopathy and mild discomfort.	150
Inhalation
12 to 41 mg/m3	Workers who operated a machine that used Hydrogen Peroxide to sanitize cardboard packaging were exposed to aerosolized Hydrogen Peroxide. Workers reported eye and throat irritation and gradual bleaching of hair. One worker developed interstitial pulmonary disease and impaired gas exchange, but since he was a heavy smoker, the cause could not be ascertained.	151
1.7 to 3.4 mg/m3 and 0.2 to 0.6 TWA (highest reading 11.3 mg/m3 for 1.5 h every morning)	Six workers who operated a machine for which Hydrogen Peroxide was used to sanitize the equipment were exposed to aerosolized Hydrogen Peroxide and its vapors for almost 3 years. Workers reported redness and burning in the eyes, blocked nose, itching and dryness in the throat, cough, and asthma symptoms. Most symptoms were worse at work and at the end of the work week. Additional symptoms included headache, protracted dry cough, and temporary loss of olfaction. Skin effects included burning and pricking of the fingers, drying of the hands and face, decrease in skin elasticity, and color change. Hair blanched and felt dry and rough. Two workers developed bronchoconstriction. Effects continued after the levels of Hydrogen Peroxide were reduced.	152
Hydrogen Peroxide (concentration and amount not specified)	A 51-year-old man was in the presence of a broken bottle fully filled with Hydrogen Peroxide. He inhaled fumes for 15 min. He experienced burning and watery eyes, and blurred vision developed (could see only shadows) over 2 h. He presented 3 days later with bilateral visual loss and reported that he was only able to see shadows in both eyes. Neuro-ophthalmological examination revealed visual acuity of 2/10 in both eyes. Direct and consensual pupillary light reflexes were decreased, extrinsic ocular motility was normal, and color perception was impaired. There was swelling of the optic discs. Other neurological examination findings were normal. The patient underwent pulse therapy of methylprednisolone and maintenance therapy of prednisone. He showed visual improvement in 6 days, but showed similar visual acuity findings and bilateral optic atrophy in 30 days.	153
90% aq. Hydrogen Peroxide vapor	Men accidentally exposed to 90% Hydrogen Peroxide vapor experienced an increased flow of saliva, scratchy feeling of the throat, and respiratory passage inflammation.	116
Other
5 x 20 mL 3% aq. Hydrogen Peroxide	An obese 54-year-old male underwent irrigation of an infected and fistulous herniorrhaphy wound with Hydrogen Peroxide. Not all irrigating volume seemed to have drained from the wound. On the fifth irrigation the patient suddenly lost consciousness, showed cardiac shock and fell into coma which lasted for 15 min. ECG showed signs of transient myocardial ischemia. The patient made a full recovery within 3 days. The authors attributed this occurrence to widespread embolization of oxygen microbubbles, especially to the cerebral and coronary arteries	154