In women, the breasts overlay the pectoralis major muscles and usually extend from the level of the second rib to the level of the sixth rib in the front of the human rib cage; thus, the breasts cover much of the chest area and the chest walls. At the front of the chest, the breast tissue can extend from the clavicle (collarbone) to the middle of the sternum (breastbone). At the sides of the chest, the breast tissue can extend into the axilla (armpit), and can reach as far to the back as the latissimus dorsi muscle, extending from the lower back to the humerus bone (the longest bone of the upper arm). As a mammary gland, the breast is an inhomogeneous anatomic structure composed of layers of different types of tissue, among which predominate two types, adipose tissue and glandular tissue, which effects the lactation functions of the breasts.

Morphologically, the breast is a cone with the base at the chest wall, and the apex at the nipple, the center of the NAC (nipple-areola complex). The superficial tissue layer (superficial fascia) is separated from the skin by 0.5–2.5 cm of subcutaneous fat (adipose tissue). The suspensory Cooper's ligaments are fibrous-tissue prolongations that radiate from the superficial fascia to the skin envelope. The adult breast contains 14–18 irregular lactiferous lobes that converge to the nipple, to ducts 2.0–4.5 mm in diameter; the milk ducts (lactiferous ducts) are immediately surrounded with dense connective tissue that functions as a support framework. The glandular tissue of the breast is biochemically supported with estrogen; thus, when a woman reaches menopause (cessation of menstruation) and her body estrogen levels decrease, the milk gland tissue then atrophies, withers, and disappears, resulting in a breast composed of adipose tissue, superficial fascia, suspensory ligaments, and the skin envelope.