Breast development usually occurs between the ages of 10 and 18. Most people start breast development at the age of 10~18 years. Usually at the age of 10~11 years, the nipple and the base of the breast below the areola begin to develop, which is mainly characterized by the nipple and areola protruding forward. Usually at the age of 12~13 years old, the whole breast begins to develop, and the breast is hemispherical and protrudes outward. Usually at the age of 14 to 15, the nipple, areola and breast will protrude forward, with the nipple and areola protruding more obviously. Usually at the age of 16 to 18, the breasts are basically fully developed. Breast development is influenced by genetic factors, nutritional factors and other aspects. In the process of development, it is important to pay attention to balanced nutrition and wear appropriate underwear.