1. Underdevelopment of the breasts According to statistics, most girls reaching the age of puberty are facing the problem of underdeveloped breasts, which can be attributed to either congenital or acquired factors. Congenital factors include functional disturbances in the parents' endocrine system due to their poor physical constitutions or illnesses, causing the lack of lactogenic hormones in the cells of the female fetus. When the child grows up to puberty, her chest becomes flat as a result of the breasts poor responses to female sex hormones. On the other hand, the root cause of acquired factors can be traced to excessive mental stress, fatigue, diseases, or dietary imbalance during a girl's puberty - the key period between the stage when her breasts start to develop and the stage of their maturity - which brings about impaired functions of the endocrine system and retarded responses of the breasts to female sex hormones. As a result, the growth of breast tissues slows down and the rate of fat accumulation declines, leading to small breast size. 2. Deformation and sagging or the loss of firmness and elasticity (a) Research shows that as many as 40% of nursing mothers suffer from deformed contours of their breasts. At any time from pregnancy to delivery and followed by breast-feeding, dietary imbalance can cause nutritional disequilibrium and damage to the breasts' fibrous tissues, resulting in shrinkage, laxation, and sagging. (b) Furthermore, giving birth too early in life, multiple deliveries and miscarriages, menstrual disturbances, and excessive menstrual flow will also lead to inadequacy of the kidneys, causing the breasts to slacken and sag. (c) The ovary functions of a woman will progressively weaken with advancing age before coming to an eventual halt, while the mammary tissues of her breasts will also shrink slowly. During menopause or after the permanent cessation of her menstruation, the tissues of the mammary glands begin to waste away while the fatty tissues continue to build up. At a later stage, when the acini of mammary glands disappears, the breast size starts to reduce, the skin loses its elasticity, and Cooper's ligaments slacken, resulting in sagging of the breast. (d) Improper way of putting on the brassiere as well as cup sizes that are either too big or too small can cause the shifting of fatty tissue or sagging of the breasts. Besides, larger than normal breast sizes due to obesity will lead to unbearable strain in the support of muscles and ligaments, resulting in the breasts sagging.