Human Milk Sharing in the United States: A Scoping Review

Abstract

Background:

Human milk is the optimal form of infant nutrition. If mother's own milk is unavailable, families may seek alternative sources of human milk through milk sharing, despite potential health and safety risks with this practice.

Objective:

The purpose of this scoping review was to synthesize the current literature on human milk sharing in the United States to help health care professionals better understand how families may use this practice for infant nutrition.

Methods:

A systematic search was conducted in June 2021 using Ovid MEDLINE, Embase, CINAHL, ProQuest Central, Web of Science, and Google Scholar. Articles were included if the primary outcome was milk sharing, excluding milk banks and preterm hospitalized infants. Results were limited to studies conducted in the United States and published in English after January 1, 2000.

Results:

From 2,124 articles, 34 met inclusion criteria and were reviewed. Study designs were largely observational (30/34), and participants were predominantly white, married, and middle-income women experiencing lactation problems or in possession of excess breast milk. Milk sharing, not for profit, was often facilitated through the internet but exchanged in person. Conversely, for-profit milk sharing often involved shipping and studies found evidence of milk contamination. No studies documented infant harm.

Conclusions:

There is limited research on the milk quality and relative risks of milk sharing, and no research on clinical outcomes in infants fed shared milk. Clinicians have opportunities to engage in open conversations about this practice to guide risk mitigation, however, research on recipient infant outcomes are urgently needed to inform best practices.

Introduction

It is well known that human milk is the optimal form of infant nutrition.¹ Both the benefits of breastfeeding and the risks of formula are well established.² Human milk confers innumerable nutritional and immunological benefits to the infant, including both short- and long-term medical and neurodevelopmental advantages.³ These advantages include protection against infection; improved cognitive development; and reduced risk of cardiovascular disease, obesity, and diabetes.^1,3 Moreover, formula has been associated with increased risk of infections, allergies, diabetes, inflammatory bowel disease, and obesity.² Thus, human milk is considered the gold standard for infant feeding and the American Academy of Pediatrics (AAP) recommends exclusive breastfeeding for the first 6 months of an infant's life.^1,3 However, mother's own milk or pasteurized donor milk from a milk bank may not always be available.

Recently, internet-based milk sharing networks popularized as a community-based social intervention to increase access to human milk.^4,5 The availability of internet-based milk sharing networks provides opportunities to increase the number of infants fed human milk. Yet, limited data are available regarding the health and safety of these practices. Furthermore, there is a lack of consensus among public health and professional organizations, which negatively affects the ability of health care professionals to provide guidance for informed infant feeding decisions.⁵ To address these gaps in knowledge, a scoping review was conducted to identify the types of available evidence on milk sharing and clarify key concepts in the literature. The primary purpose was to help health care professionals better understand the scope of milk sharing and the rationale used by families to engage in this practice. This article will add to existing literature on milk sharing by providing a framework of what is known and what types of research are needed to inform health care professionals and public health policy.

Methods

Search strategy

We conducted a systematic search in June 2021 to locate both published and unpublished research, including peer-reviewed journal articles, conference abstracts, research and committee reports, government reports, and policy documents. Due to the informal nature of milk sharing and the emerging evidence in this field, the researchers determined a scoping review would best fit this review. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist was utilized to guide this process.⁶

An initial search of PubMed was undertaken to identify articles on the topic. The text words contained in the titles and abstracts of relevant articles, and the index terms used to describe the articles were used to develop a full search strategy. Searches determined keyword and index term relevance and were adapted for each information source. The search terms included informal or peer-to-peer milk sharing, or internet purchasing of human milk, using database-specific thesaurus terms (e.g., MeSH terms) as well as keyword terms.

The databases searched included Ovid MEDLINE, Embase, CINAHL, and ProQuest Central. Additionally, using secondary keyword searches, Web of Science was used to identify potential literature published outside of traditional academic publishing, for example, theses and conference abstracts. Finally, the reference list of all included sources of evidence were screened for additional studies. This scoping review was registered to OSF Registries (Registration DOI: 10.17605/OSF.IO/VXMJP) and the full search strategy is available at https://osf.io/vxmjp

Inclusion criteria

Studies included qualitative, quantitative, descriptive, and mixed methods designs. We also incorporated conference abstracts, research and committee reports, government reports, and policy documents. Studies were included if the primary outcome was related to milk sharing, defined as the exchange of expressed milk for the purpose of maintaining an exclusive human milk diet for the term healthy infant. Expressed milk was fresh or frozen and not subject to regulation or routine pasteurization according to accepted standards. For the purposes of this review, not-for-profit milk sharing was defined as the commerce-free exchange of expressed milk and for-profit milk sharing refers to the compensated exchange of expressed milk. Internet-based milk sharing refers to the use of online networks to facilitate the exchange of expressed milk; these networks may include not-for-profit and for-profit milk sharing exchanges.

Exclusion criteria

Studies were excluded if they solely reported on milk banking, or preterm and critically ill infants. We excluded preterm and critically ill infants because the risks to these infants are greater and should be discussed separately. Results were further limited to studies conducted in the United States and published in English after January 1, 2000. Studies published before this were excluded as the practice of internet-based milk sharing did not exist until approximately 2010.⁷ Furthermore, given varying opinions on the degree of risk associated with human milk sharing around the world, studies conducted outside of the United States were excluded. Results were limited to exclude reviews, commentaries, and periodicals, as they are not primary research.

Study selection

Following the formal search in June 2021, all identified citations were collated and uploaded into EndNote 20 and duplicates were removed. The review process consisted of two levels of screening, a title and abstract review and a full-text review, performed with the online software application Rayyan.⁸ Two members of the research team (K.C.K. and A.C.A.) independently screened the title and abstract of all retrieved citations against the inclusion criteria. Any articles that were deemed relevant by either or both researchers were included in the full-text review. Next, the two researchers (K.C.K. and A.C.A.) individually assessed the full-text articles to determine eligibility. Reasons for exclusion of sources of evidence at the full-text review stage were recorded. Any discord between the researchers at each stage of the selection process was resolved by a third researcher (L.F.W.) and further disagreements were resolved through discussion until full consensus was obtained.

Data extraction

One researcher (K.C.K.) extracted the data and evaluated the methodological quality and credibility of each included study. Data were extracted using a data extraction tool developed by the researcher (K.C.K.). Extracted data included specific details about the participants, methods, limitations, clinical implications, and key findings relevant to the research question.

Data analysis

This review used the findings of each study and the primary data therein to produce a synthesis of milk sharing practices in the United States. Articles were grouped into not-for-profit and for-profit milk sharing to highlight differences. Data are presented in tabular form and categories were created to organize the results by study design, study population, outcomes measured, and key findings. A narrative summary follows the tabulated results and describes how the results relate to the research question. Potential sources of bias and limitations of each study were identified and discussed as a research team.

Results

We initially identified 2,124 articles, and 631 duplicates were removed. During the initial title and abstract screening process, the number of articles to review decreased to 117. Full-text articles were then retrieved and reviewed for inclusion. After further investigation, 34 articles met the eligibility criteria. An overview of the review process is detailed in Figure 1.

FIG. 1.

PRISMA flow diagram. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

Articles were excluded for the following reasons: intended recipients were preterm or critically ill; did not use milk sharing or used milk banking; were review articles, commentaries, or periodicals; were not written in English; conducted outside of the United States; and were duplicates. However, two articles were included in this review despite containing participants from outside the United States.^9,10 The research team determined that 90% of the study participants were from the United States and the results were pertinent to the current review.^9,10 Similarly, a few studies included in this review contained participants that were preterm or critically ill.^11,12 Again, the researchers determined that this subset of the study population was marginal in each case, and these studies were important to include in this review.

Included studies were mostly observational, descriptive studies using cross-sectional data (30/34). Study methods also included one nonrandomized controlled trial (1/34), a research report (1/34), and position statements (2/34). Almost half of the studies included were not designed to evaluate a potential relationship between milk sharing and infant health-related outcomes (16/34). Seven studies conducted research on milk quality and no studies measured clinical outcomes or long-term outcomes in infants fed shared milk.

Findings from the included studies underlined key differences between articles related to donor compensation for the exchange of expressed milk. The following sections separate articles into two categories, which are, not-for-profit milk sharing and for-profit milk sharing. Relevant studies are summarized for each section (Tables 1 and 2, respectively).

Table 1.

Not-For-Profit Milk Sharing

References	Study design	Study population (n)	Outcomes measured	Key findings
⁹	Cross-sectional observational	Interviews with mothers who received milk from internet-based milk sharing networks (n = 20)	Challenges and facilitators influencing mothers' ability to access human milk from a peer	Motivations: informed decision making and transparency (participants routinely asked potential donors questions about medical history), and support from health care professionals. Challenges: substantial effort required to secure human milk (time-consuming, travel), institutional barriers (negative feedback or perceived lack of support), milk bank-specific barriers (distance, cost, prescriptions, pasteurization, and prioritize sick/preterm infants), and lack of societal awareness and acceptance (stigma).
¹⁰	Cross-sectional observational	Interviews with mothers who received milk from internet-based milk sharing networks (n = 20)	Motivations for using milk from a peer and stress-related experiences	Participants were mostly college educated, married women, including 16 biological parents and 4 adoptive parents. Motivations: health benefits, medical need, preference over formula, and provided relief and comfort, reducing mothers' self-reported symptoms of postpartum depression and anxiety. Challenges: fear of running out and logistical stressors to secure milk.
¹¹	Retrospective observational	Blog posts from internet-based milk sharing networks regarding donor milk and milk sharing from 2010 to 2020 (n = 122)	Parental practices and perceptions of receiving and donating milk through informal and formal routes	Concerns: disease transmission (40.8%) and bacterial contamination (30.6%) with milk sharing. Milk bank donors were more likely to involve physicians than shared milk recipients (25.0% versus 2.7%). Milk bank recipients were more likely than shared milk recipients to have a medical necessity (75.0% versus 30.7%), involve physicians (75.0% versus 25.6%), and cite positive emotions (93.8% versus 61.2%).
¹²	Cross-sectional observational	Survey respondents from internet-based milk sharing networks who participated in milk sharing as a recipient (n = 205)	Factors associated with emotional responses to a parent's decision to feed their infant shared milk	Motivations: receiving strong spousal/partner support and screening health status of donor's child. Concerns: very little health risk concerns regarding disease transmission and exposure to substances that may be present in shared milk (drugs, tobacco, alcohol, toxins, and allergens). Barriers: negative social stigma and low health risk concerns.
¹³	Cross-sectional observational	Survey respondents from internet-based milk sharing networks who participated in milk sharing as a donor or recipient (n = 867)	Demographic characteristics of milk sharing participants and the structural factors associated with milk sharing practices	Respondents were primarily white, middle-class, well-educated, and employed women. Both donors and recipients reported higher than the national average for household income, maternal educational attainment, and breastfeeding exclusivity and duration. Women with lactation insufficiency achieved high rates of human milk exclusivity and duration with milk sharing.
¹⁴	Observational	Individuals who posted in internet-based milk sharing networks over 3 months (n = 954)	Size and activity of internet-based milk sharing networks	1,492 milk sharing posts were extracted from 9 states. Donors: 52.7% reported additional information, including milk attributes (87.9%), donor lifestyle (33.7%), and medication/supplement information (8.5%). Recipients: 55.7% stated why they needed milk, including lactation problems (69.4%), child's health (48.5%), adoption/fostering (13.5%), and mother's health (11.9%).
¹⁵	Observational qualitative	Direct peer-to-peer milk sharing donors and recipients across the United States (n = 165)	Moral dilemmas and experiences of milk sharing participants	Mothers nearly always sought shared milk due to an unexpected lactation crisis; some required a brief period of supplementation, over half continued breastfeeding, and others ceased breastfeeding and relied completely on milk sharing. Mothers managed stigma through secrecy and avoidance of those who might judge them.
¹⁶	Observational qualitative	Survey respondents from internet-based milk sharing networks who participated in milk sharing as a donor or recipient and volunteered for follow-on interviews (n = 27)	Motivations for sharing milk with a peer rather than a milk bank	63.0% shared milk through internet-based milk sharing networks, 40.7% with friends, 37.0% with members in their moms' groups, 33.3% with friend of a friend, 11.1% with relatives, and 3.7% with a surrogate family. Most did not intend to share milk; rather, excess milk prompted them to look for other ways to donate milk. Results highlight a strong belief in the value of breast milk, benefit of helping and connecting with families through milk sharing, and concerns and knowledge gaps about milk banks.
¹⁷	Observational qualitative	Mothers of term newborns during postpartum hospitalization at a hospital in Oregon (n = 24)	Maternal knowledge and attitudes toward different donor milk supplementation options	67.0% of mothers stated they would feel comfortable supplementing their infant's diet with milk from someone they knew. Almost unanimous mistrust of for-profit milk sharing. Concerns: safety; lack of medical screening, regulation, credibility, and quality assurance; exposure to drugs, alcohol, or dilution with cow's milk; concerns were similar to milk banking concerns.
¹⁸	Observational qualitative	Mothers from New York (n = 41)	Awareness, attitudes, and motivations for sharing milk	12.0% of mothers donated shared milk and 10.0% received shared milk. Most participants were aware of milk sharing and had positive attitudes toward it. More women were receptive to donating if their own child had enough, than to receiving it. Motivations: sufficient milk supply, excess stored milk, own child has enough milk, high value on human milk, and to help others. Concerns: donor's diet, drug use, medications, and disease status; especially with anonymous donors.
¹⁹	Observational	National sample of women from cross-sectional questionnaire (n = 456) and interviews with mothers from New York (n = 41)	Prevalence of milk sharing as well as attitudes toward for-profit milk sharing	14.0% of a national sample of women reported sharing milk (i.e., for-profit and not-for-profit milk sharing and milk banking). Milk sharing donors: 50.0% provided to a friend or acquaintance, 37.0% donated to a milk bank, and 7.4% sold milk to a stranger. Milk sharing recipients: 65.0% received from a friend or acquaintance and 3.0% purchased milk online from a stranger. Several mothers received milk from more than one source. Concerns: intentions of those who profit from the sale of human milk and treating human milk as a commodity.
²⁰	Retrospective cohort	Mothers at 12 months postpartum who delivered an infant >24 weeks at a hospital in Ohio (n = 499)	Awareness, consideration, participation, and reasons for sharing milk	77.0% of mothers were aware of milk sharing (including milk banking). Awareness was positively associated with socioeconomic status, age, white race, breastfeeding, and sufficient milk supply. Most common sources included friends, relatives, and the media. Around 25.0% of mothers considered it, 20.8% considered providing it, and 7.8% considered feeding their own infant another mother's milk. 3.8% reported sharing milk through friends, relatives, and milk banks. No reported sharing through the internet or for-profit milk sharing.
²¹	Observational qualitative	Interviews with mothers who received milk from their community and/or internet-based milk sharing networks (n = 30)	Risk perception and mitigation among peer-to-peer human milk sharing participants	Risk perception: rely heavily on trust engendered by the mother-to-mother bond. Mothers considered potential risks of milk sharing but were outweighed by the benefits of human milk and known risks of formula feeding. Risk–benefit analysis is highly personalized and informed by each parent's knowledge, values, and perceptions. Attitudes: home pasteurization is undesirable because it destroys beneficial human milk components.
²²	Cross-sectional observational	Survey respondents who self-identified as shared milk recipients from milk banks (n = 233) or internet-based milk sharing networks (n = 422)	Motivations and concerns regarding human milk sharing	Motivations: milk bank costs (53.3%), concerns about pasteurization affecting milk quality (26.5%), and inability to obtain prescriptions for milk banks (23.0%). Concerns: alcohol/drug transmission (27.5%), potential disease transmission (24.6%), and bacterial contamination (19.7%) with milk sharing. 55.9% did not have any concerns and 78.2% did not medically screen donors because they trusted them.
²³	Cross-sectional observational	Survey respondents who participated in internet-based milk sharing networks in Florida (n = 392)	Milk sharing practices, perceptions of milk sharing, and demographic characteristics	78.3% of donors and 67.2% of recipients used the internet to facilitate milk sharing, but 72.1% took place in person. 69.0% of donors and 72.7% of recipients shared milk with multiple users. Milk is frequently exchanged between strangers (91.9% of donors and 27.7% of recipients) but shipping and for-profit milk sharing was rare (1.0% of donors and 3.8% of recipients sold milk; and 4.8% shipped milk).
²⁴	Cross-sectional observational	Survey respondents from internet-based milk sharing networks who participated in milk sharing as a donor or recipient (n = 867)	Milk sharing communities, donor compensation, anonymous milk sharing, recipients' concerns about milk sharing risks, and screening practices	39.0% of recipients screen everyone, 25.9% screen only strangers, 25.9% screen some but not all, and 9.3% do not screen anyone; in comparison, 47.5% of donors do not screen anyone. Among the 21.4% of recipients who received shipped milk, 52.3% always screened donors, 25.0% screened some but not all, 18.2% screened strangers only, and 4.5% did not screen anyone. 2.0% of donors sold milk and 8.7% of recipients purchased milk; all recipients who purchased milk reported screening or meeting their donors in person.
²⁵	Cross-sectional observational	Survey respondents who participated in internet-based milk sharing networks in Florida (n = 321)	Milk sharing participants' milk storage and handling practices	Donors: 78.9% reported sanitizing pumping equipment, 82.3% reported hand washing, and 54.4% used ice when transporting milk. 8.5% reported freezing milk for >6 months and 1.5% reported leaving milk out at room temperature for >8 hours. Recipients: 80.0% reported following defrosting practices (i.e., hot water or refrigerator defrost), 64.5% reported hand washing, and 57.6% used ice when transporting expressed milk. 6.0% reported freezing milk for >6 months and 0.9% reported leaving milk out at room temperature for >8 hours, which is later given to an infant.
²⁶	Cross-sectional observational	Survey respondents who received donor milk from internet-based milk sharing networks (n = 351)	Characteristics of recipient participants and infants, donor screening practices, and related risk abatement strategies	Mostly biological mothers (89.9%) with insufficient milk supply (87.1%) seeking milk, serious infant health problem (13.8%), or congenital disorder/birth trauma (8.0%) were less common. Routine screening of donors was low, including use of medications (prescription 46.2%, nonprescription 38.3%), drugs (36.1%), tobacco (40.5%), alcohol (38.7%), health status of donor's child (46.7%), HIV test within 12 months (21.7%), Hepatitis B test within 12 months (15.1%), and Hepatitis C test within 12 months (14.8%). 16.0% of recipients reported consistent use of heat treatment. 79.1% of recipients involved partners/caregivers, 22.6% involved recipient infant's doctor, and 4.5% involved medical professionals.
²⁹	Nonrandomized controlled trial	Samples of expressed milk from mothers who were breastfeeding their own child (n = 6)	Temperature conditions and refreezing on microbial growth and milk constituents	Expressed milk that had been frozen and then thawed, undergone repeated freeze–thaw cycles, left unrefrigerated for 8 hours, or refrigerated for 24 hours, did not develop a microbial load approaching 10⁴ CFU/mL.
³⁰	Observational cohort	Samples of expressed milk from mom directly, shared milk, screened raw donor milk, and unpasteurized banked milk (n = 121)	Macronutrient, antimicrobial protein, and bacteria composition by method of milk exchange	12.4% of samples had total bacteria levels above 10⁵ CFU/mL, 24.8% had total bacteria levels above 10⁴ CFU/mL, and 16.5% of samples were positive for coliform. No evidence of differences in lactose, fat, water, lysozyme activity, IgA activity, aerobic bacteria, coliform, and Staphylococcus aureus between exchange methods. No evidence of water dilution.
³¹	Cross-sectional observational	Survey respondents from internet-based milk sharing networks and blogs for mothers with low milk supply (n = 475)	Characteristics and outcomes of those with low milk supply who used shared milk to meet at least 10.0% of their infant's milk needs	29.1% of mothers with low milk supply reported shared milk use; and 59.3% of these mothers were still feeding their infants breast milk at 6 months, compared with 39.6% of nonusers. For women with lactation insufficiency, shared milk users were more likely to breastfeed longer, seek resources, identify healthful options, and report greater satisfaction.
⁴²	Retrospective observational	Articles related to milk sharing from U.S. print newspapers (n = 30)	Representations of milk sharing in contemporary news media in the United States	Complex and contradictory images of human milk; with banked milk represented as ‘liquid gold,’ safe and beneficial to babies, and practices of donating to milk banks framed as altruistic and morally commendable. In comparison, shared milk was framed as playing ‘Russian roulette,’ intrinsically risky and potentially dangerous practice that is ill informed and irresponsible.
⁴³	Observational	Survey respondents from internet-based milk sharing networks (n = 392) and interviews with milk sharing participants in Florida (n = 30)	Milk sharing participants' reaction to media representations of the Pediatrics article by Keim et al.³⁴	48.0% of participants had heard of the Pediatrics article by Keim et al.,³⁴ 43.5% of participants rejected its findings' applicability to their own practices, and 54.5% expressed skepticism. They distinguished the sale/purchase from the free exchange of breast milk, highlighted the importance of hygiene and proper milk handling practices, and the critical role of trust.

IgA, immunoglobulin A.

Table 2.

For-Profit Milk Sharing

References	Study design	Study population (n)	Outcomes measured	Key findings
³²	Cross-sectional observational	Advertisements posted in internet-based milk sharing networks over 1 week (n = 254)	Health and safety risks of internet-based milk sharing practices	Postings came from four websites: Only the breast (42.0%), HM4HB (39.0%), Eats on Feets (13.0%), and milk share (7.0%). For-profit milk sharing only occurred on only the breast. 69.0% of postings were providing milk, through not-for-profit (26.0%) or for-profit (57.0%). 51.0% of providers mentioned limiting/abstaining from drugs, 40.0% reported infectious disease status or screening, and 20.0% reported hygiene and handling practices.
³³	Cross-sectional observational	Samples of milk anonymously purchased through the internet (n = 102)	Cost, outside box, packing materials, milk container, temperature, and condition of milk samples	2,131 oz of milk was bought for $8,306 (mean of $1.47/oz). The mean surface temperature for the milk containers was 2°C; 89.0% arrived above −20°C and 45.0% above 4°C. The surface temperature was associated with cost of shipping, time in transit, and condition of milk containers. 63.0% of the boxes contained dry ice and 19.0% had no cooling agent.
³⁴	Cross-sectional observational	Samples of milk anonymously purchased through the internet (n = 101) and unpasteurized samples donated to a milk bank (n = 20)	Microbial contamination of milk samples	74.0% of samples were colonized with Gram-negative bacteria or had >10⁴ CFU/mL total aerobic count. 17.0% of samples had bacteria counts >10⁶ CFU/mL. Growth of most species was positively associated with days in transit. No samples were HIV RNA positive. 21.0% of internet samples and 5.0% of the milk bank samples were CMV DNA positive.
³⁵	Cross-sectional observational	Samples of milk anonymously purchased through the internet (n = 102)	Presence of human or bovine DNA in milk samples	All samples contained human DNA and 10.8% of samples also contained bovine DNA. 10/11 samples were classified as “high positive” (i.e., consistent with human milk mixed with ≥10.0% fluid cow's milk or formula).
³⁶	Cross-sectional observational	Samples of milk anonymously purchased through the internet (n = 102)	Exposure to 13 common classes of drugs of abuse in milk samples	No samples tested positive for the selected drugs of interest and no sellers admitted to illicit drug use in their advertisement. 71.0% of sellers stated abstaining from some type(s) of drugs (prescription or illicit) in their advertisement.
³⁷	Cross-sectional observational	Samples of milk anonymously purchased through the internet (n = 102)	Levels of caffeine, nicotine, and its metabolite, cotinine, in milk samples	97.0% of samples had detectable levels of caffeine. 58.0% of samples had detectable levels of nicotine, or its metabolite cotinine, with 4.0% having levels high enough to indicate active smoking.

HM4HB, Human Milk 4 Human Babies.

Not-for-profit milk sharing

Milk sharing participants were predominantly white, married, middle income, educated, and employed women experiencing lactation problems or in possession of excess breast milk.^13–20 Participants were motivated by the known health benefits of human milk and its superiority over formula.^10,21 Participants were also driven by the benefit of helping and connecting with families through milk sharing.¹⁶ Additionally, they were motivated by barriers to milk banking; for example, costs, prescriptions, and pasteurization since it destroys beneficial human milk components.^21,22

Not-for-profit milk sharing was often facilitated through internet-based milk sharing networks (Human Milk 4 Human Babies, Eats on Feets, and Milk Share), yet the physical exchange of human milk often occurred in person.^23,24 Research showed donors reported providing frozen milk as well as fresh milk through local, in-person delivery, and less often shipped frozen milk.²⁴ Milk was exchanged among family and friends, but also frequently between strangers.²³ Most participants reported following safe milk handling practices, such as hand washing and sanitizing equipment.²⁵ Few participants reported heat treatment upon receipt of the milk.²⁶

The most common concerns of women not participating in milk sharing included disease transmission, contamination, exposure to drugs, or dilution with cow's milk.^17–19 However, most participants had few or no concerns and did not medically screen donors because they trusted them.^12,21,22 In addition to limited donor medical screening, several studies reported minimal involvement of health care professionals in milk sharing.^11,22,24,26 Studies also highlighted challenges families faced; for example, logistical stressors and effort to secure milk, fear of running out, institutional barriers, and social stigma.^9,10,12 In response, participants avoided physicians, family, and friends who might judge them.¹⁵

No studies have documented infant harm, including two case studies, in which there were also no reports of milk contamination associated with not-for-profit milk sharing.^27,28 Furthermore, research has shown that samples of expressed milk under various ambient temperature conditions did not develop a microbial load approaching 10⁴ CFU/mL.²⁹ Another study found no evidence of differences in macronutrient, antimicrobial protein, and bacteria composition by method of human milk exchange.³⁰ Moreover, milk sharing has the potential to help infants meet the AAPs breastfeeding goals.^13,31 One study reported higher rates of exclusivity and duration of human milk feeding among milk sharing participants than the national average.¹³ Similarly, research found more participants using shared milk were feeding their infants human milk at 6 months than nonusers.³¹ The potential benefits of not-for-profit milk sharing are evident, although there is a lack of research on the milk quality and relative risks of not-for-profit milk sharing.

For-profit milk sharing

While several internet-based milk sharing networks exist, the for-profit sale of human milk was found on one website (i.e., Only the Breast).³² This study revealed 5.0% of participants reported for-profit milk sharing solely to make money.³² Statements about donors' diet, exercise, drug use, milk handling practices, and milk quality were associated with the sale of human milk.³² These findings support differentiating for-profit milk sharing, where milk was purchased from anonymous donors and shipped to strangers, from not-for-profit milk sharing.

Five studies included in this review were published from research on human milk samples purchased anonymously online.^33–37 The investigators excluded milk samples from individuals who inquired additional information about the recipient, to maintain anonymity. The first study found milk samples shipped without ice and milk leaking out of plastic bags upon arrival.³³ Subsequently, these same investigators found evidence of bacterial contamination and bacterial growth was associated with days in transit.³⁴ The high prevalence of bacterial growth was likely due to improper storage conditions, although the milk samples included in this study were shipped to an off-site mailbox that was only accessible 6 days a week.³⁴ Next, the researchers discovered bovine DNA in several samples, suggesting cow's milk adulteration.³⁵ They also reported detectable levels of caffeine and tobacco metabolites in the majority of samples.³⁷ Nevertheless, they found no evidence of drugs of abuse in the milk samples and no samples were positive for HIV-RNA.^34,36

Discussion

Milk sharing participants navigate lactation problems and limited access to breast milk obtained from milk banks to provide infants with an exclusive human milk diet.^13,31 Those involved in milk sharing place a high value on human milk and this practice ultimately supports breast milk continuation and exclusivity.^13,31 Yet, the Food and Drug Administration and the AAP do not recommend milk sharing.^38–40 Whenever human milk is expressed and handled, there is a risk of contamination.^28,39 Human milk is a bodily fluid and can carry medications, drugs, and other substances.^28,39 Viral, bacterial, and fungal transmission through human milk is also possible, the most concerning of which are HIV, Hepatitis B, and Hepatitis C.^28,39 To reduce these risks, the Academy of Breastfeeding Medicine has recommended donor medical screening and safe milk handling practices.⁴¹ In addition, home pasteurization can further reduce the risk of infections, however, it decreases some nutritional and immunological components of human milk as well.⁴¹ Home pasteurization is also complicated and may be difficult to practice in certain settings without access to uniform heating sources.

Milk sharing practices can incorporate a combination of the following: community-based (sharing between friends or relatives) or internet-based (connecting through online networks), not-for-profit or for-profit, and direct in-person exchanges or shipping milk. Thus, the possible health and safety risks may vary based on individual practices. Currently, the potential risks to the infant fed shared milk are inferential and no studies have documented infant harm. It is unknown if internet-based milk sharing, for-profit milk sharing, or shipping milk increase the level of risk associated with this practice, as comparative studies would permit outcome analyses. Moreover, internet-based milk sharing is not synonymous with anonymous exchanges of expressed breast milk. Internet-based milk sharing may be associated with increased risk of exposure to medications or infectious diseases if there is no donor medical screening involved. However, studies also found limited donor medical screening among community-based milk sharing and exchanges with friends and relatives.^21,22

Nonetheless, this review identified evidence of potential harm from for-profit milk sharing and especially when shipping is involved. For-profit milk sharing donors face different incentives than not-for-profit milk sharing donors. Consequently, included studies found evidence of milk dilution and contamination with cow's milk associated with for-profit milk sharing.³⁵ This research also found evidence of bacterial contamination associated with shipping milk.³⁴ Although these studies involved for-profit milk sharing, not-for-profit milk sharing can also involve shipping milk. Therefore, the potential risk of contamination is also relevant to not-for-profit milk sharing practices that involve shipping milk. Health care professionals have opportunities to understand how families may use milk sharing for infant nutrition to explain potential risks. Understanding that individual practices may vary, clinicians should consider the known benefits of human milk and the possible health and safety risks when facilitating patient-centered discussions with families concerning infant feeding decisions.

Limitations

There are a few limitations of this scoping review; first, this review was limited to milk sharing for the term healthy infant. Although the search strategy and study selection process used in this review were rigorous, the data extraction and analyses were performed solely by one researcher (K.C.K.). Nonetheless, the data extraction was supervised by an experienced research librarian (A.C.A.) and the analyses were discussed with an experienced researcher in breastfeeding medicine (L.F.W.). Lastly, this review was limited by the external validity of the available research on milk sharing. Current studies are largely observational, descriptive studies and prevalence reports. However, the exact prevalence of milk sharing in the United States remains unknown due to a lack of population-level studies. Consequently, the limited generalizability of these studies restricts the ability to fully assess risk mitigation of milk sharing practices.

Conclusions

This review highlights the complexity of milk sharing practices. For-profit milk sharing in the included studies involved shipping frozen milk, which was frequently contaminated upon arrival.³⁴ Conversely, not-for-profit milk sharing was often facilitated through internet-based networks but exchanged in person, which may decrease the time milk is exposed to improper storage conditions.^23,24 Without further studies, for-profit and not-for-profit milk sharing remains an important distinction, as the former may involve dilution with cow's milk. An arguably equally important distinction for the clinician is whether the milk is exchanged in person or shipped, since there is evidence of potential harm of bacterial contamination with shipping milk. Furthermore, anonymous milk sharing may preclude the ability to screen donors for infections or medications.

Health care professionals have an opportunity to affirm milk sharing relationships and engage in shared decision making to counsel families about risk mitigation strategies such as donor medical screening and safe milk handling practices. Unfortunately, there is limited research on milk quality and the potential risks of this practice by examining milk samples, and no research on infant health outcomes. Consequently, the lack of clinical research may inadequately quantify the health and safety of this practice. Additional research is imperative to inform public health policy, but recruitment will require overcoming the secrecy and nondisclosure to health care professionals. Future collaborations with organizations that promote milk sharing may be beneficial.

Footnotes

Acknowledgment

The authors thank Rosie Frasso, PhD, MSc, MSc, CPH, Jefferson College of Population Health, for her support with study conception.

Authors' Contributions

K.C.K., L.F.W., and A.C.A. contributed to study conception, study design, data collection, and data interpretation. K.C.K. had primary responsibility for writing the article. All authors reviewed, edited, read, and approved the article.

Disclosure Statement

L.F.W. serves as the Associate Editor of Breastfeeding Medicine. K.C.K. and A.C.A. have no conflicts of interest to report.

Funding Information

No funding was received for this article.

References

Eidelman

, Schanler

. Breastfeeding and the use of human milk. Pediatrics, 2012; 129:e827–e841.

Brent

The risks and benefits of human donor breast milk. Pediatr Ann, 2013; 42:84–90.

Granger

, Embleton

, Palmer

, et al. Maternal breastmilk, infant gut microbiome and the impact on preterm infant health. Acta Paediatr, 2021; 110:450–457.

Sullivan

CG.

Position statement regarding use of informally shared human milk. Nurs Outlook, 2016; 64:98–102.

Palmquist

AEL

, Perrin

, Cassar-Uhl

, et al. Current trends in research on human milk exchange for infant feeding. J Hum Lact, 2019; 35:453–477.

Tricco

, Lillie

, Zarin

, et al. PRISMA extension for scoping reviews (PRISMA-ScR): Checklist and explanation. Ann Intern Med, 2018; 169:467–473.

Akre

, Gribble

, Minchin

. Milk sharing: From private practice to public pursuit. Int Breastfeed J, 2011; 6:1–3.

Ouzzani

, Hammady

, Fedorowicz

, et al. Rayyan—Intelligent Systematic Review, 210 ed. Rayyan, Hyderabad, India, 2016.

McCloskey

, Karandikar

. A liberation health approach to examining challenges and facilitators of peer-to-peer human milk sharing. J Hum Lact, 2018; 34:438–447.

10.

McCloskey

, Karandikar

. Peer-to-peer human milk sharing: Recipient mothers' motivations, stress, and postpartum mental health. Breastfeed Med, 2019; 14:88–97.

11.

Kuznetsova

, Sood

, Milanaik

. An analysis of parental opinions of human milk sharing options. Pediatrics, 2020; 146:144–145.

12.

Schafer

, Ashida

, Palmquist

AEL

. Psychosocial dimensions of human milk sharing. Matern Child Nutr, 2018; 14(Suppl 6):e12606.

13.

Palmquist

, Doehler

. Contextualizing online human milk sharing: Structural factors and lactation disparity among middle income women in the U.S. Soc Sci Med, 2014; 122:140–147.

14.

Perrin

, Goodell

, Allen

, et al. A mixed-methods observational study of human milk sharing communities on Facebook. Breastfeed Med, 2014; 9:128–134.

15.

Tomori

, Palmquist

, Dowling

. Contested moral landscapes: Negotiating breastfeeding stigma in breastmilk sharing, nighttime breastfeeding, and long-term breastfeeding in the U.S. and the U.K. Soc Sci Med, 2016; 168:178–185.

16.

Perrin

, Goodell

, Fogleman

, et al. Expanding the supply of pasteurized donor milk: Understanding why peer-to-peer milk sharers in the United States do not donate to milk banks. J Hum Lact, 2016; 32:229–237.

17.

Rabinowitz

, Kair

, Sipsma

, et al. Human donor milk or formula: A qualitative study of maternal perspectives on supplementation. Breastfeed Med, 2018; 13:195–203.

18.

O'Sullivan

, Geraghty

, Rasmussen

. Informal human milk sharing: A qualitative exploration of the attitudes and experiences of mothers. J Hum Lact, 2016; 32:416–424.

19.

O'Sullivan

, Geraghty

, Rasmussen

. Awareness and prevalence of human milk sharing and selling in the United States. Matern Child Nutr, 2018; 14(Suppl 6):e12567.

20.

Keim

, McNamara

, Dillon

, et al. Breastmilk sharing: Awareness and participation among women in the Moms2Moms Study. Breastfeed Med, 2014; 9:398–406.

21.

Peregoy

, Rasmussen

, Pinheiro

, et al. Milk sharing: A case of comparative risks. In: 19th Internation Society for Research in Human Milk and Lactation (ISRHML) Conference; 2018. Kanagawa, Japan. Abstracts in Breastfeeding Medicine: Breastfeeding Medicine, 2018.

22.

Kuznetsova

, Sood

, Heffern

, et al. Where to get donor breast milk? Self-reported parental motivations and concerns regarding the choice of informal milk sharing versus milk banks. Pediatrics, 2020; 146:143–144.

23.

Reyes-Foster

, Carter

, Hinojosa

. Milk sharing in practice: A descriptive analysis of peer breastmilk sharing. Breastfeed Med, 2015; 10:263–269.

24.

Palmquist

, Doehler

. Human milk sharing practices in the U.S. Matern Child Nutr, 2016; 12:278–290.

25.

Reyes-Foster

, Carter

, Hinojosa

. Human milk handling and storage practices among peer milk-sharing mothers. J Hum Lact, 2017; 33:173–180.

26.

Bond

AB.

Risk abatement practices of recipient participants in private arrangement milk sharing in the United States [Doctoral Dissertation]: Arizona State University, 2016.

27.

McNally

, Spatz

. Mothers who engage in long-term informal milk sharing. Am J Matern Child Nurs, 2020; 45:338–343.

28.

Martino

, Spatz

. Informal milk sharing: What nurses need to know. Am J Matern Child Nurs, 2014; 39:369–374.

29.

Rechtman

, Lee

, Berg

. Effect of environmental conditions on unpasteurized donor human milk. Breastfeed Med, 2006; 1:24–26.

30.

Perrin

, Fogleman

, Davis

, et al. A pilot study on nutrients, antimicrobial proteins, and bacteria in commerce-free models for exchanging expressed human milk in the USA. Matern Child Nutr, 2018; 14(Suppl 6):e12566.

31.

Cassar-Uhl

, Liberatos

. Use of shared milk among breastfeeding mothers with lactation insufficiency. Matern Child Nutr, 2018; 14(Suppl 6):e12594.

32.

Keim

, McNamara

, Jayadeva

, et al. Breast milk sharing via the internet: The practice and health and safety considerations. Matern Child Health J, 2014; 18:1471–1479.

33.

Geraghty

, McNamara

, Dillon

, et al. Buying human milk via the internet: Just a click away. Breastfeed Med, 2013; 8:474–478.

34.

Keim

, Hogan

, McNamara

, et al. Microbial contamination of human milk purchased via the internet. Pediatrics, 2013; 132:e1227–e1235.

35.

Keim

, Kulkarni

, McNamara

, et al. Cow's milk contamination of human milk purchased via the internet. Pediatrics, 2015; 135:e1157–e1162.

36.

Keim

, McNamara

, Kwiek

, et al. Drugs of abuse in human milk purchased via the internet. Breastfeed Med, 2015; 10:416–418.

37.

Geraghty

, McNamara

, Kwiek

, et al. Tobacco metabolites and caffeine in human milk purchased via the internet. Breastfeed Med, 2015; 10:419–424.

38.

Use of donor human milk

U.S

. Food & Drug Administration: U.S. Food & Drug

Administration; 2018

. https://www.fda.gov/science-research/pediatrics/use-donor-human-milk (accessed January 23, 2022).

39.

Abrams

, Landers

, Noble

, et al. Donor human milk for the high-risk infant: Preparation, safety, and usage options in the United States. Pediatrics, 2017; 139:1–6.

40.

Abrams

. Healthy Children

Healthychildren

.org: American Academy of

Pediatrics

. 2022 [updated 5/27/2022]. https://healthychildren.org/English/tips-tools/ask-the-pediatrician/Pages/Are-there-shortages-of-infant-formula-due-to-COVID-19.aspx?_gl=1*uua6k2*_ga*NzcxOTA0ODQ2LjE2NTI5NzY4NDU.*_ga_FD9D3XZVQQ*MTY1Mjk3Njg0NC4xLjAuMTY1Mjk3Njg0NC4w&_ga=2.210816279.300911655.1652976845-771904846.1652976845 (accessed June 1, 2022).

41.

Sriraman

, Evans

, Lawrence

, et al. Academy of Breastfeeding Medicine's 2017 position statement on informal breast milk sharing for the term healthy infant. Breastfeed Med, 2018; 13:2–4.

42.

Carter

, Reyes-Foster

, Rogers

. Liquid gold or Russian roulette? Risk and human milk sharing in the US news media. Health Risk Soc, 2015; 17:30–45.

43.

Reyes-Foster

, Carter

. “That's not the milk sharing I'm doing”: Responses to a Pediatrics article from women who milk share. Hum Organ, 2018; 77:262–272.