Why Do Men Have Nipples?

Evolutionary Relic or Functional Organ?

There is a reasonable, biological explanation as to why women have nipples: To feed babies. Why men have nipples remains less clear.

The Darwinian theory of natural selection would seem to dictate that male nipples serve no real purpose and, as such, should have been bred out of the human species by now. Of course, they haven't been, and this has to do with the foundations of how a human being develops in the uterus before they're born.

This article retraces what happens during fetal development to form nipples in males and discusses the extent to which they serve any function. It also delves into two common male nipple abnormalities.

A father holding a daughter in a swimming pool
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Fetal Development

The answer is simpler than you think. During the development of an embryo after fertilization (embryogenesis), females and males both start from the same genetic base.

In the initial weeks, there is no differentiation between the biological sexes, even as the embryonic cells continue to divide and specialize. Nipples are already developing at this time.

Embryos are the same until week six or seven, when the sex genes—called the X and Y chromosomes—dictate whether the baby will be born female or male. Both sexes have one X chromosome. A second X chromosome defines a female. An additional Y chromosome defines a male.

It is that Y chromosome that leads to the development of the testes in males. By contrast, female embryos undergo changes in the mammary cells, starting with the development of a pit at the center of each nipple. This pit will gradually form a depression that connects to a lactiferous (milk-producing) duct.

While this happens to some degree in males, it is far less profound and developed.

Function of the Male Nipple

While male nipples are sometimes thought to be vestigial—meaning that they have become functionless in the course of evolution, much like the appendix or wisdom teeth—that is largely untrue. They may be more accurately described as remnants of fetal development. But even this suggests that male nipples serve no real purpose.

The nipple, in fact, contains a dense supply of nerves that function as a major stimulatory organ. As such, it can be considered a secondary sex characteristic in men, along with facial hair and an Adam's apple.

The stimulatory response in men (and women) appears to be unique to the human species. It could potentially have evolutionary value in that it contributes to the desire to reproduce.

This said, the nerve network in the male nipple is much denser than that in the female nipple, meaning that sensory response tends to be more discreet.

Male Nipple Abnormalities

Some characteristics associated with the female breast and nipple can abnormally occur in the male breast and nipple, too. Some are the result of the dysregulation of hormones, while others may be due to genetics.

Galactorrhea

While men will not produce milk under usual circumstances, the male breast can lactate if under the influence of the hormone prolactin.

The condition, known as male galactorrhea, often occurs as a result of a medication or medical condition that triggers a drop in male hormones (primarily testosterone) and an increase in female hormones.

Hormonal changes are commonly associated with women, but they also occur in men. For example, while women go through menopause, men undergo andropause and a drop in the hormone testosterone when they're in their 40s.

One such example is the drug Motilium (domperidone), which not only treats lactation problems in women but can be used in men to treat nausea, vomiting, gastroparesis, and Parkinson's disease.

Other causes include malnutrition, pituitary gland disorders, hypothyroidism (low thyroid function), and frequent nipple stimulation.

Gynecomastia

Gynecomastia is the enlargement of male breasts that commonly occurs in older men as testosterone levels progressively drop with age. In addition to the general swelling of breast tissue, gynecomastia can trigger the enlargement of the nipples and surrounding areolas.

Gynecomastia can also affect boys and younger men. In some cases, particularly in adolescent boys undergoing puberty, the condition is temporary. Other common causes include:

  • Adrenal or pituitary gland tumor
  • Anabolic steroid use
  • Cancer chemotherapy
  • Hypothyroidism
  • Kidney failure
  • Prostate medications like Propecia (finasteride) and Aldactone (spironolactone)
  • Tricyclic antidepressants

Gynecomastia is associated with an increased risk of breast cancer in men. While rare, breast cancer in men is most commonly detected by the formation of a hardened lump under the nipple and areola.

Summary

Males have nipples because of the way that embryos develop in the initial weeks after gestation. Those eventually born female and male are the same until sex chromosomes are defined, which doesn't happen until week six or seven of pregnancy. Nipples begin to develop before that time.

Like the appendix and wisdom teeth, male nipples are widely assumed to be functionless. They don't supply nourishment to newborn babies, but male nipples contain a dense supply of nerves that function as a major stimulatory organ.

Frequently Asked Questions

  • How do male nipples differ from female nipples?

    Typically, the nipples of both sexes are virtually indistinguishable until puberty, during which time they undergo distinctive changes. Male nipples tend to end up being smaller than female nipples. There is also less variation among male nipples than female nipples.

  • Do men get turned on by nipple stimulation?

    For around half of men, the nipples are an important erogenous zone. Some experts suspect this means male nipples serve an evolutionary function by playing a role in the desire to mate and reproduce. Some research suggests nipple stimulation fires up areas of the brain related to genital arousal.

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7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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