Hello, experts from Guangzhou Huamei Plastic Surgery Hospital said: On the one hand, breast size is determined by genetic and physical factors, such as race, mother's condition and personal fatness. On the other hand, it is influenced by acquired factors, such as food nutrition, bodybuilding, hormone secretion and some diseases. Teenage breasts. Development is closely related to hormones in the body. The anterior pituitary gland produces hormones that promote breast development and directly act on the breast. Ovary produces estrogen and progesterone to promote breast growth; Growth hormone and insulin are also indispensable components of breast development. Therefore, flat chest has a great relationship with malnutrition and low estrogen secretion.