The exterior of all humans’ breasts are basically the same; however, the size, shape, and function of breasts vary significantly between the sexes. The key parts of the female breast include:

• Breast: The larger, more pronounced part of the breast is typically visible through clothing. Some cultures associate breast size with sexuality, and others view a woman’s breast size as a sign of maturity and fertility.
• Areola: This circular area around the nipple typically has darker or deeper pink colored skin. The color can change over time due to hormonal changes associated with menstruation, menopause, and pregnancy.
• Nipple: The protruding tip of the breast, the nipple is where milk is dispensed. It is also the site of many nerve endings. Typically, each breast has one, but in rare cases more than one may be present.

At the onset of puberty, female sex hormones — particularly estrogen — dictate breast growth. It’s these hormones that manifest women’s larger breast size compared to that of men.

A woman’s larger breasts and erect nipples during sexual stimulation are part of her secondary sex organs, that is, characteristics related to reproduction but not directly involved in it. However, many proponents of breast-feeding argue that the breast is a vital part of the reproductive process.

During pregnancy, a woman’s breasts will enlarge due to an increase in hormones as well as the body’s preparation for milk production. Normal changes in the breast during pregnancy can include firming, enlarged nipples, darker nipples, and stretch marks on the skin due to enlargement.

A woman’s breast size may also increase due to using hormone-based contraception, such as birth control pills, patches, or intravaginal devices.

Another difference between the breasts of men and women are the amount of nerve endings in the nipples and surrounding tissues. The increased nerve endings signal milk production in mothers and can also provide a greater chance for sexual arousal when the nipples are stimulated.

Women are more prone to problems with their breasts. These problems can include:

• Breast cancer
• Breast infection
• Benign breast lumps
• Mastalgia, or breast pain
• Hypoplasia, or failure of one or both breasts to develop
• Virginal breast hypertrophy, or premature development of large breasts

Women over the age of 40 are encouraged to do self-breast exams monthly and get a mammogram at least once a year. Early detection for breast cancer and other breast problems makes them easier to treat.