Nipples develop before an embryo’s sex characteristics develop. Male nipples may not play an evolutionary role, but they’re not purposeless, either—for some, nipples are involved in sexual arousal.
Male nipples exist because nipples begin to develop in all embryos before sex differentiation occurs in the womb.
Sex differentiation is the process in which an embryo’s cells take on specific functions and male or female characteristics begin to develop according to the embryo’s genetic instructions. Whereas nipples begin to develop around week 6, sex differentiation occurs around week 7.
The changes that start in males around week 7 occur due to the activation of the SRY gene, also known as the sex determination gene. This activation will eventually lead to the development of male reproductive organs. Meanwhile, the cells that have already formed early nipples remain intact, developing fully in both males and females.
Male nipples are not designed for breastfeeding or chestfeeding. However, male nipples serve a purpose in sexual arousal, which some experts believe may have an evolutionary purpose. Men have a dense supply of nerves in their nipples that can stimulate sexual arousal, which, in turn, may encourage them to be intimate and reproduce.
Until puberty, the nipples in both males and females are generally similar. When puberty hits, nipples undergo distinct changes. Female nipples begin to grow larger while male nipples, though growing, do not typically undergo as many changes.
Several conditions can affect male nipples, due to genetics, hormonal imbalances, or other factors. They include:
- Gynecomastia: When there is an imbalance of the hormones testosterone and estrogen, males may develop gynecomastia, or enlarged breast tissue. It can affect one or both breasts. Medications, drug use, and health conditions may also contribute to gynecomastia.
- Galactorrhea: This condition occurs when milk or a milk-like discharge leaks from a man’s nipples. While sometimes harmless, the condition can develop due to medication side effects or pituitary gland disorders that increase the body’s levels of prolactin, the hormone that stimulates milk production.
- Male breast cancer: Rarely, men can develop breast cancer. About 1% of diagnosed breast cancers occur in men. Cancer may cause a lump or a thickening of the breast tissue near the nipple. Other signs include inverted nipples, nipple discharge, or changes in the skin surrounding the nipple.
