Science Explains Why Men Can’t Lactate (But Sometimes Do)

It’s all about their hormones.

Originally Published: 
A bare-chested father holding his baby.

All men have nipples and mammary glands, and most have the desire to bond with their babies and give their partners a breastfeeding break. Alas, you cannot milk a cisgender man — dad nipples are merely decorative. But that doesn’t mean men are technically unable to produce milk. In fact the scientific evidence suggests that it could happen, under the right conditions.

“Brace yourselves, guys. Science is demolishing your last excuses,” Pulitzer-prize winning physiologist Jared Diamond wrote, somewhat ominously, in Discover back in 1995. “We’ve known for some time that many male mammals, including some men, can undergo breast development and lactate under special conditions,” Charles Darwin agreed. “It is well known that in the males of all mammals, including man, rudimentary mammae exist,” he wrote in 1871. “These in several instances have become well developed, and have yielded a copious supply of milk.”

You heard the man. Copious.

In order to understand why men can lactate but usually don’t, we need to take a trip back to the embryonic stage. Human embryos all start out pretty much the same, until the fourth week of gestation when the genes on chromosome 23 kick in, creating sex differences. But before those sex differences get going, the sexless embryo has already developed mammary glands — which is why, no matter how you turn out, you’re stuck with nipples.

Cut to puberty, when the pituitary gland helps those mammaries mature in females. The result is that female mammaries become primed for breast milk production at puberty, so that any spike in the hormone prolactin causes them to lactate.

Male nipples remain woeful duds.

So cis men come into this world with all the right hardware for the job, but puberty sets dads-to-be down the wrong path for milk production. When a man does lactate (and yes, it happens) it is almost always a symptom of an underlying medical problem (or thanks to injections of estrogen and prolactin, which come with a slew of side effects).

Male lactation is a known side effect of anabolic steroids and thorazine, an antipsychotic medication. Pituitary tumors and cirrhosis of the liver can also make men produce milk. In fact, any time the liver is compromised there’s risk of male lactation, because a healthy liver’s job is to absorb spare hormones, and an imbalance leads to too much prolactin floating around. Soon after being rescued from POW camps in World War II, some men lactated because their hormones resumed producing prolactin once they were fed, but their livers had still not recovered from the trauma.

Still, past claims from medical anthropologist Dana Raphael (echoed by endocrinologist Robert Greenblatt) that men could breastfeed if they stimulated their nipples long enough seem highly unlikely. And if a man is able to achieve this by simple suckling, that may be a sign of an underlying condition. “It could be that you have this man with this pituitary tumor and he produces milk once the baby starts suckling,” Dr. Jack Newman told Scientific American.

Plus, there are probably better uses of your time — and your nipples.

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