Men have nipples because nipples form in the womb before an embryo develops male or female sex characteristics. By the time the body “decides” to become male, the nipples are already in place, and there’s no evolutionary reason to get rid of them.
Nipples Form Before Sex Differentiation
Every human embryo follows the same basic blueprint for its first several weeks of development. During this early period, structures like nipples, milk lines, and the surrounding skin begin taking shape regardless of whether the embryo carries XX or XY chromosomes. The gene on the Y chromosome that triggers male development doesn’t activate until around the sixth or seventh week of gestation. By that point, the groundwork for nipples has already been laid.
From there, breast development continues on a nearly identical path for both sexes throughout the rest of pregnancy. The surrounding areola forms around the fifth month, and the nipple itself takes its final shape during the third trimester. Prenatal breast development does not differ between genders. Male and female newborns have the same nipple anatomy at birth. The divergence only happens later, during puberty, when rising estrogen levels cause female breast tissue to grow and develop functional milk-producing glands.
Why Evolution Never Removed Them
If male nipples serve no purpose, you might expect evolution to have eliminated them over millions of years. But evolution doesn’t work like an engineer tidying up unused parts. It works through selection pressure: traits disappear only if they actively reduce survival or reproduction. Male nipples don’t do either. They cost almost nothing in terms of energy or resources, so there’s never been a reason for natural selection to act against them.
Biologist Stephen Jay Gould coined the term “spandrel” to describe biological features that exist not because they were directly selected for, but because they come along for the ride with something else that was. Male nipples are considered the textbook example. Women’s nipples are under strong selective pressure because they’re essential for breastfeeding. Since both sexes share the vast majority of their genetic code, the developmental instructions for nipples get passed along to everyone. The nipples men have are simply a byproduct of the developmental blueprint that produces functional nipples in women.
Interestingly, research comparing male and female nipple size found that women’s nipples are significantly more variable in size than men’s. This makes sense: female nipples interact with infants during breastfeeding, so they’re shaped by more complex selective forces. Male nipples, under no such pressure, tend to cluster around a narrower range of sizes.
What’s Actually Inside a Male Nipple
Male nipples aren’t just skin. They contain real anatomical structures, just in an underdeveloped state. Internally, men have rudimentary milk ducts that never fully form, along with blood vessels and connective tissue. What they lack is the glandular tissue that, in women, produces milk.
One thing male nipples do have in abundance is nerve endings. Nipples contain hundreds of them, making them one of the most sensitive areas on the body. This nerve density is why nipple stimulation can trigger sexual arousal in men, which is arguably the closest thing male nipples have to a functional role in adult life.
Can Men Actually Lactate?
Technically, yes, though it’s rare and almost always a sign of a medical problem. Male lactation requires abnormally high levels of prolactin, the hormone that drives milk production. In one documented case, a man with a prolactin-secreting pituitary tumor had prolactin levels roughly 25 times the normal upper limit. He produced a white discharge from his nipples, which resolved once the tumor was treated and his hormone levels returned to normal.
About 80% of women with prolactin-secreting tumors experience milk production, but the same condition is uncommon in men. The reason is that men normally have very low prolactin and higher testosterone, which suppresses lactation. It takes a dramatic hormonal shift to override that balance.
Breast Tissue Changes Men Should Know About
Because men have breast tissue, even in its underdeveloped form, that tissue can respond to hormonal changes throughout life. Gynecomastia, a noticeable swelling of breast tissue in men, is surprisingly common. It frequently shows up during puberty, when hormone levels are in flux, and typically resolves on its own within six months to two years. It becomes common again later in life: somewhere between 24% and 65% of men aged 50 to 80 experience some degree of breast tissue enlargement, though most never notice symptoms.
More seriously, men can develop breast cancer. It’s rare, accounting for about 1 out of every 100 breast cancer diagnoses in the United States, but it does happen. Because men don’t expect breast problems, male breast cancer tends to be caught at a later stage. A hard lump near the nipple, changes in nipple shape, or discharge are all worth getting checked out, regardless of how unlikely the cause may seem.