Breasts are mainly composed of skin, nipple, breast tissue, fat and other structures. Physiological knowledge mainly includes the normal development of breasts and the cyclic changes with menstruation. Breasts are located in front of the chest wall of 2-6 ribs, with nipple and areola in the center, skin on the surface, and mammary tissue and breast suspensory ligament on the deep surface of the skin. The mammary tissue consists mainly of milk ducts and alveoli, which form the lobules of the mammary gland and then converge radially to the nipple by the milk ducts. Breasts usually erupt at puberty (around 10 years of age) and develop into mature breasts over time, when ductal development predominates. After pregnancy, estrogen and progesterone cause the ducts and follicles to further develop and mature, and they become capable of lactation. After delivery, lactation begins under the stimulation of lactogen and suckling. After the mammary glands mature, they change with the menstrual cycle. Before and during menstruation, there may be a slight swelling and pain, which is usually alleviated after menstruation. Breast fibroma, breast hyperplasia, breast cancer and other high incidence of breast disease, it is recommended that women over 45 years of age regular breast examination, usually have discomfort in a timely manner to consult a doctor.