During puberty, estrogen production and growth in the glands is the major influence on breast growth. Breast development is completed after ovulation begins to occur regularly in the teen years. Most women notice cyclical changes to their breasts due to fluctuations in hormones. These affect the size, firmness and tenderness of the breasts. Before menstruation, for example, the breasts may swell and become tender.
During pregnancy, hormones prepare the breasts for milk production. The growth of the mammary glands and ducts produces swelling of the breasts. Veins in the breasts may appear on the surface of the skin, which has stretched to accommodate the development of internal breast glands. As women go through menopause, the mammary glands and breasts lose their firmness.