The breasts are made up of fat, connective tissue and glandular tissue which contains lobes. The lobes are where breast milk is produced. A network of ducts connects the lobes to the nipple.

A woman's breasts are rarely the same size as each other, and may feel different at different times of the menstrual cycle, sometimes becoming lumpy just before a period.

Under the skin, an area of breast tissue extends into the armpit (axilla). The armpits also contain a collection of lymph glands (also called lymph nodes), which are part of the lymphatic system. There are also lymph nodes just beside the breastbone and behind the collarbones.