Breast Anatomy & Physiology - Puberty

When the woman begins to menstruate, the breasts undergo a periodic premenstrual phase that varies with the individual but can include an increase in size, swelling and tenderness

In response to hormone stimulation, the breasts enlarge due to the growth of ductal and alveolar tissues and an increase in fat deposits. The nipple and areola also enlarge and become more sensitive to touch. When the woman begins to menstruate, the breasts undergo a periodic premenstrual phase that varies with the individual but can include an increase in size, swelling and tenderness. The symptoms subside within a few days of the onset of bleeding. During pregnancy, the breasts increase in size dramatically due to the influence of progesterone, and the nipple and areola become deeply pigmented and increase in size also. The necessary machinery to produce milk by late pregnancy replaces most of the fat. After delivery the breasts begin to secrete milk and the gland rapidly returns to the pre-pregnant state when nursing ceases. The postmenopausal breast may retain its shape, but the milk producing machinery is mostly replaced by fat.
 
The consistencies of breast lobes vary from woman to woman and may even vary in an individual from one side to the other. However, in general, the glandular portion of the breast has a firm, slightly nodular feel to it. Surrounding the lobes is breast fat. Unlike the lobes, the fat is almost always soft. The discrepancy in textures between these two components allows one to outline the lobes by carefully palpating (feeling) the breast.
 
The breasts of younger women are primarily composed of glandular tissue with only a small percentage being fat. Thus they are firmer than in older counterparts. As women age, especially with the loss of estrogen at menopause, the lobes involute (shrivel) and are replaced by fat. The breasts become softer and lose their support.
 
Whereas female hormones influence all components of the breast, the glandular tissue is most sensitive. Very dramatic and totally normal changes can occur in the consistency of the breasts during the menstrual cycle. These changes are most evident just prior to menstruation when levels of estrogen and progesterone are peaking. Right after menstruation, hormone levels are at their lowest, and the breast becomes softer and less tender.
 
In postmenopausal women, who are not taking estrogen supplementation, weight becomes a significant factor n the size and appearance of the breasts. Being mostly composed of fat at this point small changes in body weight can produce significant changes in breast size.