Earlier this month, the United States Supreme Court declined to hear a sex discrimination case from an Iowa woman who wanted to pump milk at work. The Court’s reasoning? It’s not sexist to tell women they can’t lactate at work because men can also lactate.

Which…what? Is it really possible for men to lactate? Can it happen naturally? As it turns out, yes, it can, and it’s more likely in human men than in the vast majority of mammals. That said, don’t worry, fellas. You’re highly unlikely to start sprinkling milk out of the blue.

Let’s start with why women, and not men, lactate routinely in appropriate circumstances. As you might suspect, the cause is genetic—22 of the 23 pairs of human chromosomes are identical, with the 23rd pair the only set that differs between the sexes.

“The genes on chromosome 23, acting in concert with genes on other chromosomes, ultimately determine all differences between our sexes,” wrote Pulitzer Prize winner and one-time physiologist Jared Diamond in a 1995 article for Discover. “Those differences, of course, include not only the possession of ovaries as opposed to testes but also the postadolescent differences in beards, pitch of voice, and breast development.”

All male and female mammals have mammary glands, which is the organ that produces milk. When mammary glands mature fully in females during puberty, they develop into a state where a hormonal spike—most notably of prolactin—can easily induce lactation. For males, the gland generally doesn’t mature to that level.

So the difference is a matter of hormonal influence, first during puberty and then again after pregnancy. Men do have the necessary equipment, but usually they don’t naturally produce the necessary levels of hormones to use it. Provide the right hormones, though, and male lactation is absolutely possible.

One way to do this is through medical intervention. There are a number of ways this can be done, but generally, you need to introduce both estrogen and prolactin into the system, often by injection. Some drugs, like Thorazine—an antipsychotic popular in the mid-20th century—and the heart medication digoxin have induced milk from men as a side effect.

But how can men develop milk naturally?

The circumstances, as you might guess, are rare. One way to induce lactation from men is via starvation. During World War II, thousands of men reported lactation while held as prisoners either in Japanese POW camps or Nazi concentration camps. When a person is malnourished, the hormone-producing glands—like the pituitary gland, which generates prolactin—are impeded, but so too is the hormone-destroying liver. If proper nourishment is later provided, the glands recover much more quickly than the liver, causing hormone levels to skyrocket.

It’s also possible that something could target the pituitary gland and cause it to produce more prolactin. As breast-feeding expert Jack Newman notes, a tumor on the pituitary gland could have this effect.

There’s also a camp within the scientific community that thinks men can lactate merely through nipple stimulation. In 1978, medical anthropologist Dana Raphael claimed as much in her book The Tender Gift: Breastfeeding. Medical College of Georgia endocrinologist Robert Greenblatt later agreed with Raphael. Diamond, too, thinks this is possible.

“Mere repeated mechanical stimulation of the nipples suffices in some cases, since mechanical stimulation is a natural way of releasing hormones,” Diamond wrote. “For instance, sexually mature but virgin female marsupials can regularly be stimulated to lactate just by placing another mother’s young on their teats.”

Diamond provided several cases “in which [not pregnant] women succeeded in nursing an infant by repeatedly placing it at the breast.” Most adoptive mothers, for instance, begin lactating within three or four weeks of adoption, suggesting mere stimulation can induce enough hormonal action to produce milk. The same has reportedly happened to men, including a 38-year-old man in Sri Lanka who, in 2002, nursed his two daughters through infancy after his wife died during childbirth, according to an Agence France-Presse report.

So is it possible for men to lactate? Yes, it is. Does it happen often? Not at all. Could it happen more? Absolutely, if men decide they want the job.

“Soon, some combination of manual nipple stimulation and hormone injections may develop the confident expectant father’s latent potential to make milk,” Diamond said. “While I missed the boat myself, it wouldn’t surprise me if some of my younger male colleagues, and surely men of my sons’ generation, exploit their opportunity to nurse children.

“The remaining obstacle will then no longer be physiological but psychological: Will all you guys be able to get over your hang-up that breast-feeding is a woman’s job?”