Breasts generally begin to develop around the age of 9-14 years old, the specific development time varies from person to person and is mainly divided into five stages according to the different degrees of development of the three parts of the nipple diameter, areola size and breast shape. 1. Stage 1: Breasts are just starting to develop, nipples are usually below 3mm, areola is flat, usually before 9 years old. 2. Stage 2: the diameter of the nipple and areola increases, and the areola bulges outward toward the breast, and the bulging areola can be touched, usually between 8 and 9 years old. 3. Stage 3: The average nipple value reaches 4mm, the diameter of the areola increases, and the breast is raised and not limited to the inside of the areola, usually between 11-12 years old. 4. Stage 4: The three parts of the nipple, areola, and breast further increase in size, and the nipple and areola continue to protrude and show a clear demarcation line from the breast, on average around 12 years of age. 5. Stage 5: The nipple diameter reaches 7mm or more, the breasts are mature and show no obvious difference from mature women, on average between 14 and 16 years old. Breast development is related to a variety of factors, there are individual differences, daily life to carry out a reasonable diet, increase nutrition, ensure adequate sleep, is conducive to promoting breast development and physical health.