In our beauty-loving society, breasts are one of the focal points of concern for the majority of women as well as many men. From the basic structure and function of the breast, the physiological changes of the normal female breast, to the daily care of the breast, both men and women should have a comprehensive understanding of the basic knowledge of the breast for their own or their family’s health. The basic structure and function of the breast The adult unproductive breast is hemispherical in shape, starting from the second rib and ending at the sixth rib, and located horizontally between the edge of the sternum and the mid-axillary line. The shape of the breast is highly variable and is influenced by regional, ethnic, familial, and physiological cycles. During pregnancy and lactation, the breasts increase in size; after stopping lactation, the mammary glands revert and the breasts become smaller; in old age, the breasts atrophy and sag. The coat of the breast is none other than our skin, which is symmetrical, smooth and flat, just like the skin of our its parts. (Once breast disease occurs, this coat of the breast is likely to undergo specific changes that we can see with our eyes and need to be taken seriously.) At the center of the breast is the nipple and the areola that surrounds it with a deepened color. The skin of the nipple and areola is thin and susceptible to injury and infection. The nipple is rich in sensory nerve endings, and caressing it during sex can be an effective way to stimulate sexual desire. The soft and elastic breast tissue that is usually touched is the main component of the breast, especially in young women. After women enter their 40s, the overall level of estrogen released by the ovaries decreases and the breast tissue gradually shrinks and is replaced by soft fatty tissue, giving it a sagging appearance, just like the fat that accumulates in our abdomen and waist, which is a physiological phenomenon. The surface of the breast tissue and its deeper surface are covered with a thin, white envelope. They are suspended from the chest wall by many short ligaments, which we call “Cooper’s ligaments”. As the name implies, these ligaments play a role in suspending and lifting the breast tissue, giving the breast a glossy curved appearance. When these ligaments are invaded by a lesion in the breast, they can shorten further, causing a depression in the skin of the bare breast, like a dimple on the face, hence the medical term “dimple syndrome”. Women with dimples should seek prompt medical attention from a breast specialist. In the deeper part of the breast tissue are muscles, mainly the pectoralis major, pectoralis minor, serratus anterior and latissimus dorsi. The male breast tissue is basically receding after birth, limited to the areola area remaining a little breast tissue, generally little development, so the deep side of the male skin is these muscles. The pectoralis major muscle will be more obvious in men who work out regularly. The pectoralis minor, on the other hand, is relatively small, on the deep side of the pectoralis major and is covered by the entire pectoralis major. There is a loose gap between the breast tissue and the pectoralis major muscle, called the “posterior breast gap”, which is one of the locations for breast augmentation implants. Behind the pectoralis major muscle is the rib cage and chest wall. Let’s summarize, the order of breast structure from superficial to deep is: skin -> breast glandular tissue -> posterior breast gap -> muscle. The breast glandular tissue is rich in fat, fibrous tissue, blood vessels, nerves and lymphatic vessels. Breast lymph mainly returns to the lymphatic terminus through the axillary lymphatic vessels, and a small portion can return through the parasternal, contralateral breast, subdiaphragmatic and subperitoneal lymphatic channels. And the metastasis of breast cancer cells often takes place through the lymphatic channels. There are many lymph nodes on the lymphatic channels, which are like checkpoints on the highway. However, when cancer cells enter the lymphatic channels, they will destroy the lymph nodes in the corresponding locations, which clinically manifests as enlargement of lymph nodes. Lymph node metastasis of breast cancer often occurs in the armpit, which is one of the reasons why lymph node dissection is performed in breast cancer patients.