An unlikely market has emerged in recent years, driven by converging forces of parental anxiety, medical research, and the remarkable connectivity of the internet: the buying and selling of human breast milk.

The demand side comes primarily from two groups. One is parents of premature or medically fragile infants who cannot or do not produce sufficient breast milk and have been counseled by physicians that human milk — with its immunological properties and digestibility — is significantly better than formula for vulnerable babies. The other is a smaller but growing group of parents of healthy infants whose mothers cannot breastfeed and who are willing to pay a premium for donated or purchased milk.

Informal milk sharing has existed as long as wet nursing has existed, which is to say for most of human history. What is new is the online marketplace that has made it easy to connect sellers with buyers across geographic distances. Platforms and Facebook groups dedicated to breast milk exchange operate in a gray market — not quite legal commerce, not quite charitable donation, but something in between.

The medical establishment is cautious. Human milk from unknown donors carries potential risks — infectious disease transmission, contamination, adulteration. Formal milk banks, which process and test donated milk before distribution, exist specifically to address those risks, but demand consistently exceeds their supply, and prices are high enough that many families cannot access them.

The informal market persists because the need is real and the official channels cannot meet it. The debate about how to regulate it — or whether the regulatory costs would simply drive it further underground — is unresolved.