The maelstrom of hormones that help a woman give birth to her baby also tell her body to start producing milk. When the baby then sucks at her nipple, it stimulates the release of the hormone prolactin, which tells her body to produce more. Even so, it can take several days for milk to come in. For mothers of preemies—as well as first-time mothers and those whose babies were delivered by Caesarean section—the milk supply can take even longer to start.

On the other hand, mothers can find themselves producing more milk than their baby needs, especially if they use an electric breast pump. This has given some the option of sharing the milk their child doesn’t need; human-milk banks take the excess and give it to those who do. But as more parents and hospitals seek to use pasteurized donated milk, HMBANA banks have begun experiencing shortages. For-profit milk-banking companies have sprung up, and milk can be bought and sold online, with fewer or no checks on quality or contamination. It’s becoming a lot more complicated than simply sharing.

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In 2015, Sarah Keim, an epidemiologist at Ohio State University, published an analysis of 102 samples of breast milk she’d purchased online. Eleven had significant amounts of cow’s milk. “That is a concern,” she says. “We were surprised to find the extent of that problem.” Once money becomes involved, she adds, it becomes more likely that people will adulterate breast milk to make a quick buck.

Sharing breast milk is not new. Women have done it for millennia, letting friends’ or relatives’ hungry children nurse at their own breasts. Other times, women would hand-express their milk into pots or jars to give to families in need. And wet nurses, often impoverished or enslaved women, were often used to provide milk for wealthy children, even if it came at their ability to nurse their own. In the early 1900s, hospitals and charities began freezing and banking breast milk for sick babies.

But even with a bank as the middleman, donating breast milk is still a transaction between two mothers. The question: Should women who donate milk to these banks be compensated? And more than that, does paying for donated milk change the nature of the relationship between the women involved?

Laura Breiling / Mosaic

In 2011, Afrykayn Moon, then 32 years old, was nearly arrested for breastfeeding on a city bus in Detroit, Michigan. What angered her the most wasn’t the bus driver calling the police but rather the response she got from other mothers: “I was getting emails from people telling me how horrible a mother I am for wanting to breastfeed and doing it in public,” she says. “I had a lot of people who were actually surprised that a black woman was breastfeeding, period. They didn’t know we still do that.”

It is true that fewer black mothers in the US breastfeed than white and Hispanic mothers—59 percent of black mothers versus 75 percent of whites and 80 percent of Hispanics. In Detroit, only 40 percent of mothers ever even plan to breastfeed their children. Determined to change this, Moon founded Breastfeeding Mothers Unite to educate black women in Detroit about the health benefits of breastfeeding in the hopes that more of them would do so.