The process of breast development during puberty is related to the action of some relevant hormones in the body, among which estrogen and progesterone produced by the ovaries are the most direct factors stimulating breast development. Under the stimulation of estrogen, the epithelial cells of the breast ducts divide and proliferate, the ducts lengthen longitudinally and form branches, and the terminal ducts form the basal buds of the glandular lobules, which will later develop into glandular lobules. After ovulation of the follicle, the corpus luteum is formed and will produce progesterone. Under the combined effect of estrogen and progesterone, the ductal-lobular-glandular follicle structure gradually develops and completes. Puberty in girls generally begins at the age of 10-12 years. Visually, the nipples protrude just after puberty, but the areolas are not pigmented. around the age of 11, glandular structures now appear below the areola and the breasts begin to rise from the chest. Around the age of 13, the areola widens, the pigmentation increases, and the nipple and areola begin to protrude from the breast in a conical shape. After about 2 years, the breasts develop a smooth appearance and the base of the nipple and areola no longer protrude. Breast development can vary greatly from girl to girl. The progression of bilateral breast development can also be slightly different. The early stages of breast development can be somewhat painful and the local breast tissue is often nodular at first, so it should not be mistaken for a lump and removed. Some nodules can also appear in the later stages of breast development. Currently, with the improvement of nutritional status, the first menstruation and breast development of girls have appeared earlier, in addition, some drugs, health products and drinks may also have some influence on breast development, parents are advised to avoid giving these things to their children. More than half of boys can also develop some degree of breast development during puberty, mainly manifested as small disc-shaped nodules under the nipples and areolas, and some may be more obvious with mild pain. They can occur unilaterally or bilaterally, mostly disappearing on their own after 1-2 years, and generally do not require treatment.