Breast - Development

Development

The basic morphological structure of the human breast – female and male – is determined during the prenatal development stage. For a girl in puberty, during thelarche (the breast-development stage), the female sex hormones (principally estrogens) promote the sprouting, growth, and development of the breasts, in the course of which, as mammary glands, they grow in size and volume, and usually rest on her chest; these development stages of secondary sex characteristics (breasts, pubic hair, etc.) are illustrated in the five-stage Tanner Scale. During thelarche, the developing breasts sometimes are of unequal size, and usually the left breast is slightly larger; said condition of asymmetry is transitory and statistically normal to female physical and sexual development. Moreover, breast development sometimes is abnormal, manifested either as overdevelopment (e.g. virginal breast hypertrophy) or as underdevelopment (e.g. tuberous breast deformity) in girls and women; and manifested in boys and men as gynecomastia (woman's breasts), the consequence of a biochemical imbalance between the normal levels of the estrogen and testosterone hormones of the male body.