Although the breasts of non-pregnant women are generally considered inactive, they undergo cyclic changes associated with normal ovulation. Many women experience a premenstrual increase in breast size and density. Many women also feel breast tenderness in relation to these changes. This slight engorgement is probably due to tissue edema (holding water in the tissue). Older women who have fibrotic lumps may experience an increase in pain, usually along the perimeter of the breast mass. The volume and density changes are thought to be resultant of the changing levels of estrogens and progesterone during the menstrual cycle.

Hormone therapy, such as birth contraceptives, can also influence breast density. A constant inrush of estrogens and progestins can simulate premenstrual breast changes, often making the breasts tender. During menopause the changes in gonadotropins, estrogens and progesterone induce changes in both glandular and ductal components. Without hormone replacement therapy, the number and size of the glandular elements decrease and the volume of the breast becomes smaller. Likewise, there is a loss of contour due to the decrease in structure.

As we have seen, the lack of internal anatomical support of the breast structures requires some type of external support. Excessive movement of the breasts during physical exercise may increase this need for some women because of the structural changes during pregnancy and menstruation