Breast

The breast is a gland located on the front of the chest in mammals. It consists of milk-producing tissue, milk ducts, fat, and connective tissue. This organ represents the defining feature of mammals: offspring are nourished by milk produced by the breast.

Both men and women have breasts, but in women the breast develops during puberty and produces milk after pregnancy and childbirth. In men, the breast remains undeveloped and does not produce milk, although the basic tissue structures are present.

Structure

Inside the breast is a system of lobes, each divided into smaller lobules. These lobules contain tiny milk-producing units called alveoli. Milk travels through ducts that converge and open at the nipple. The darker area surrounding the nipple is called the areola. The space between the milk-producing tissues is filled with fat; the size of the breast generally depends on the amount of this fat.

Development and hormones

Breast development is regulated by hormones, particularly estrogen and progesterone. Puberty brings enlargement of the ducts and accumulation of fat. During pregnancy, the hormones prolactin and oxytocin prepare the milk-producing tissue and trigger milk release when the infant nurses. After menopause, the milk-producing tissue decreases.

Lactation

The primary biological function is nourishing the infant. In the days following birth, the breast produces a fluid called colostrum, which is rich in immune factors. This is followed by mature milk. International health organizations recommend that infants be breastfed from birth, citing nutritional and immune benefits.

Health and disease

The breast can be affected by various conditions: soreness and inflammation (mastitis), typically related to lactation; benign lumps such as fibroadenoma and cysts; and breast cancer. Breast cancer is one of the most common cancers in women. Early detection—through self-examination, clinical examination, and mammography—is used to identify the disease at an earlier stage.

Social aspects

In many societies, the breast carries cultural and religious significance beyond its biological function. Laws and customs regarding the covering or display of the breast vary widely between countries. There are also various surgical modifications (reduction, enlargement, or reconstruction after cancer) performed for both health and aesthetic reasons.