The preadolescent breast (known medically as stage 1 per Tanner's sex maturity ratings) consists of a small elevated nipple with no significant underlying breast tissue. (Tanner's stages are based on studies of white English girls. An American survey found that black girls tended to advance more quickly.) Genital and pubic hair development is also classified by Tanner.Puberty
begins (usually between ages of 8 and 13, average age is 11) with the development of breast tissue and pubic hair. With the hormonal changes of puberty, breast buds form. This second stage "stage 2" of breast development is the breast bud stage. Here, there is elevation of the breast and nipple as a small mound; the areola begins to enlarge. Milk ducts inside the breast begin to grow. In
stage 3, there is further enlargement and elevation of the breast and areola (with no separation of their contours) The areola begins to darken in color. The milk ducts give rise to milk glands that also begin to grow. Next,
there is projection of the areola and nipple to form a secondary mound (stage 4). In
the mature adult breast (stage 5), there is projection of the nipple only (though in some woman the areola continues to form a secondary mound). The
breasts of an aging woman diminish in size as the milk glands degrade. The breasts often become more saggy as this occurs and as the effects of gravity pull the breast tissue downwards.