Summer Topics on Breastfeeding

Topical Insect Repellants and Insecticides

The most common insect repellant is diethyltoluamide (DEET), but other insect repellants available in the United States include citridiol, icaridin (picaridin), and IR3535. Citridiol is a synthetic version of the chemical in the lemon eucalyptus tree; icaridin and IR3535 are also synthetic. Although none of these agents has been specifically studied in breastfeeding women, both the U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention (CDC) judge that they are safe during breastfeeding when used according to directions. The CDC goes further in stating that nursing mothers should use an insect repellant if they are in an area where mosquito-borne viral infections are prevalent. CDC recommends using products with ≥20% DEET on exposed skin, but DEET efficacy tends to plateau at a concentration of ∼50%, so higher concentrations are not needed. Combined sunscreen–insect repellents are not recommended. Use separate products, applying sunscreen first, followed by repellent. Limited data show that DEET-containing insect repellents applied over sunscreen decrease the sun protection factor of the sunscreen by one-third; if both products used, sunscreen should be reapplied more frequently.

Many drugs used for lice and scabies are environmental contaminants and can be found in breast milk. Nevertheless, treatment of these infestations often requires their use. Because <2% is absorbed after topical application of pyrethrins and permethrin, their rapid metabolism to inactive metabolites, and safe application directly on infants' skin, these products are acceptable in nursing mothers. Malathion appears to be poorly absorbed after topical application for lice, but until more data become available, other agents are preferred. ¹

No information is available on the use of spinosad during breastfeeding, but it is not systemically absorbed after topical application, so it should not be present in breast milk. The topical suspension contains benzyl alcohol. High doses of benzyl alcohol are potentially toxic to neonates, and the manufacturer states that mothers concerned about benzyl alcohol could pump and discard breast milk for 8 hours. This is probably unnecessary because it is very unlikely that amounts used in the treatment of head lice reach toxic levels in breast milk.

Sulfur 5–10% in a petrolatum base is safe for topical use in infants <2 months of age. ² This makes it a useful alternative to organic insecticides for nursing mothers with scabies; however, the petrolatum base makes it undesirable for use on the breast.

Topical application of lindane by mothers can increase lindane levels in milk for at least several days. It is a persistent environmental contaminant, and possibly has estrogenic effects that could decrease lactation as well as affect the nursing infant. Lindane should not be used during breastfeeding. ²

Sunscreens

The major concern with sunscreens is that some ultraviolet (UV) filters used in sunscreens cause endocrine disruption in animals. Alterations in sex hormones have been the most publicized, but alterations in thyroid function have also been reported. ³ Because of these effects, some UV filters have been banned in various jurisdictions. For example, the UV filter enzacamene (not available in the United States) is banned in children's products in Denmark. Octinoxate (also called 2-ethylhexyl-4-methoxycinnamate or octyl methoxycinnamate) has been put on the European Union's Water Directive's Framework Watch List. The sale of octinoxate and oxybenzone will be banned in Hawaii starting in January 2021 because they are thought to contribute to the bleaching of coral through an estrogenic mechanism.

Two recent studies by the Food and Drug Administration (FDA) have found that surprisingly large amounts of organic sunscreens are found in the serum of users after as little as one application and can persist for up to 3 weeks.^4,5 The articles make the point that their findings do not indicate that individuals should refrain from the use of sunscreen.

So, do these chemicals reach the breast milk? As early as 1995, reports began emerging on the detection of certain UV filters in breast milk. Out of six women tested in Germany, four had oxybenzone in their milk and two had octinoxate. The concentration ranges were 16–417 ng of oxybenzone per gram of fat and 28–47 ng per gram of fat for octinoxate. ⁶ In 2008 and 2010, two studies in Switzerland of 34 and 53 women found that 15% of women had detectable oxybenzone in their milk, 18–20% had detectable enzacamene, 38–78% had detectable octinoxate, 47–67% had detectable octocrylene, and 2–3% of women had detectable padimate A or 3-benzylidine camphor in their milk. Overall, of the 53 women in one study, 85% had at least one sunscreen detectable in their milk.^7,8 Smaller studies in Spain also found sunscreens in breast milk in a high percentage of women. Oxybenzone was found in 90–100% of subjects, benzophenone-1 in 60% of subjects, benzophenone-6 in 40% of subjects, enzacamene in 33% of subjects, and 4-hydroxybenzophenone in 33% of mothers' milk.^9,10 Most of the concentrations that have been found in milk are far above the 0.5 ng/mL level of concern for plasma concentrations by the FDA. ⁵ The threshold value of 0.5 ng/mL is based on the assessment that the level would approximate the highest plasma level below which the carcinogenic risk of any unknown compound would be <1 in 100,000 after a single dose. So it includes a large margin of safety.

Several factors make it hard to predict how much of these chemicals will be in a specific woman's breast milk. Milk concentration depends on the concentration of the chemical in the product, how much is applied, how large an area of skin it is applied to, and how often. Topical application of sunscreens to the skin is thought to result in absorption of ∼2% of the applied amount with intact skin, although there may be considerable interindividual variation. Higher percentages can be absorbed by swallowing products that are applied to the lips such as lipstick and lip balm, although the volumes of these products are relatively small. In some studies, women who reported no use of sunscreens had UV filters found in sunscreen products detectable in their milk. In addition to personal care products, many plastics, building materials, and fabrics have other UV filters incorporated into them to protect them from breakdown by UV light.

The concern with these chemicals in breast milk is that they might have endocrine disrupting developmental effects in the breastfed infant. Although individual agents have been studied in the milk of animals, any one cosmetic product might contain several different UV filters. Other than the finding that all organic UV filters are present in serum and most appear in breast milk, the mixtures have not been studied well. There is some evidence that the combination of several chemicals might have additive effects that result in toxic effects not seen with a single ingredient. ¹¹

Although animal studies clearly show that many sunscreens are endocrine disruptors, the effects on breastfed infants, if any, are not known. One group of authors state that because of the wide human exposure in combination with the clear endocrine disruptive effects observed in a large number of well-designed studies, the UV filters enzacamene, oxybenzone, and octinoxate can be considered as substances of high concern in relation to human risk. ¹¹

Two inorganic mineral products suggested as alternatives to organic sunscreens are titanium dioxide and zinc oxide. These are the only products currently considered safe and effective by the FDA in liquid (but not aerosol) formulations. These two sunscreens are available as nanoparticle formulations that do not cause the intense white color on the skin.

Summary and Conclusions

The use of personal care products poses some potential risks to the breastfed infant because they can enter the breast milk. Summer tends to be a time when more of these products are used on the skin because of exposure to insects and sun. The extent to which they enter the milk depends on many factors, but the extent of use by the mother is a major modifiable factor. Application of these products to the nipple and other areas where the infant might directly ingest the product by licking should especially be avoided.

The use of long-sleeved shirts and long pants, avoiding areas where mosquitoes are present at dusk can decrease the need for extensive use of insect repellants. For sunscreen products, good alternative products are avoiding sun exposure during the mid-day peak UV hours, sitting in shaded areas such as under umbrellas, and wearing sun-protective clothing, such as wide-brimmed hats, long sleeves, and long pants. Much more information is needed before clear guidelines can be provided as to the safest products to use, but sunscreen products containing octinoxate and oxybenzone (and enzacamene, where it is available) should probably be avoided during breastfeeding. Using products containing zinc oxide or titanium dioxide can minimize the exposure to the sunscreens of concern.