Why do men have nipples if they can't breastfeed?

The short answer

Men have nipples because all embryos start developing the same way, and nipples form before sex-specific genes activate. They likely remain simply because there’s no evolutionary pressure to remove a harmless trait.

The long answer

Great thinkers like Darwin, Aristotle, and you have pondered the question: Why do men have nipples if they can't breastfeed?

It all starts with how human embryos develop in the womb. For the first six weeks of gestation, male and female embryos develop identically, with no sex-specific traits. Around six weeks, sex-specific genes found in the X or Y chromosome flip on and put embryos on the path to being male or female.

Where do nipples come in? Well at around 5.5 weeks — just before the embryo's sex genes activate — a pair of milk or mammary ridges form on the skin extending from the armpit to the thigh. These milk ridges will eventually recede to leave (*usually) two nipples in both male and female embryos.

"​FIGURE 4​" (modified) by Schwartz et al. is licensed under ​CC BY 4.0​.

In short, nipples start forming in human embryos before sex-specific genes are activated. After that point, females will develop female traits, while males will develop male traits. Both sexes keep breast tissue and nipples thanks to this early milk ridge formation.

"​Human Embryo, Carnegie stages 10-23​" (modified) by ​Dr Mark Hill​.

Now we know how nipples develop in male humans. But why hasn't evolution removed them if they seemingly serve no purpose?

Theory #1: There's no harm in males keeping their nipples.

Some argue that male nipples remain not because they have an evolutionary advantage, but simply because they have no evolutionary disadvantage. When a trait is useful in one sex, as nipples are for nursing in females, and harmless in the other sex, there's no benefit in removing them.

Nipples aren't even the only part of male anatomy that develops by default in the embryo before sex differences kick in. The prostate contains a tiny, nonfunctional structure called the prostatic utricle. It is a remnant of embryonic Müllerian ducts, which develop into the uterus and fallopian tubes in females.

Theory #2: Nipples contribute to the desire to reproduce in males.

It's also possible that nipples do serve an evolutionary advantage in male humans. Nipples contain a dense network of nerves, making them a highly stimulatory organ. Some researchers think their role in sexual pleasure helps boost the desire to reproduce.

Theory #3: Nipples allow for the possibility of male lactation.

While rare, some male mammals are capable of lactation. The dayak fruit bat, a very rare bat species found in southeast Asia, can produce milk in both male and female bats. The exact evolutionary advantage is unclear, but dad bat may take the pressure off of mom bat from feeding the baby bat all the time.

Source: ​Alchetron​

Interestingly, human males are technically capable of lactation if there is a medication or medical condition that triggers an increase of the hormone prolactin. In these rare cases, males can produce milk. So, while far fetched, it's possible nipples haven't disappeared in males because it leaves the door open for male lactation.

🧠 Bonus brain points

Can you be born with extra nipples?

Yes, around one in 20 people have what's called supernumerary nipples. These extra nipples are leftovers from mammary crest development, rarely functional, and often appear to look like nothing more than a small mole.

"​20060726 supernumerary nipples​" (modified) by ​Per Erik Strandberg​ is licensed under ​CC BY-SA 2.5​.

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Sources

Geggel, L. (2017, June 17). Why Do Men Have Nipples?. LiveScience. https://www.livescience.com/32467-why-do-men-have-nipples.html

Green, H. (2013, December 20). Why Do Men Have Nipples?. YouTube. https://www.youtube.com/watch?v=8DnHyn_QgOE

iNaturalist. (n.d.). Dayak fruit bat (dyacopterus spadiceus). iNaturalist. https://www.inaturalist.org/taxa/40975-Dyacopterus-spadiceus

Johnson, M. (2019, February 25). Why Do Men Have Nipples? And 8 Other Questions, Answered. Healthline. https://www.healthline.com/health/mens-health/why-do-men-have-nipples

Kennard, J. (2025, September 4). Why Do Men Have Nipples?. Verywell Health. https://www.verywellhealth.com/why-do-men-have-nipples-2328794

Maria, C. S. (2012, September 4). Why Do Men Have Nipples?. HuffPost. https://www.huffpost.com/entry/why-do-men-have-nipples_n_1847460

McCarthy, S. (1999, June 8). Why do men have nipples?. Salon.com. https://www.salon.com/1999/06/08/nipples/

Moscova, M. (n.d.). Why do men have nipples?. UNSW Sites. https://www.unsw.edu.au/newsroom/news/2019/09/why-do-men-have-nipples

Simons, A. M. (2003, September 17). Why do men have nipples?. Scientific American. https://www.scientificamerican.com/article/why-do-men-have-nipples/