Breast development can begin at various ages, due to heretary and hormonal reasons. Breasts contain over 1000 lobes that create the shape and weight of breasts.
The breast is the upper ventral region of the torso of a primate, in left and right sides, containing the mammary gland which in a female can secrete milk used to feed infants. Both men and women develop breasts from the same embryological tissues. However, at puberty, female sex hormones, mainly estrogen, promote breast development, which does not occur in men, due to the higher amount of testosterone. As a result, women's breasts become far more prominent than those of men. During pregnancy, the breast is responsive to a complex interplay of hormones that cause tissue development and enlargement in order to produce milk. Three such hormones are estrogen, progesterone and prolactin, which cause glandular tissue in the breast and the uterus to change during the menstrual cycle. Each breast contains 1520 lobes. The subcutaneous adipose tissue covering the lobes gives the breast its size and shape.
Contributions by Spute, Jfdwolff, and Alison.