The breasts are made up of fat, connective tissue and glandular tissue that contains lobes. These are shown in the diagram below. The lobes are where breast milk is produced. A network of milk 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 (lymph nodes), which are part of the lymphatic system. The lymphatic system is a network of lymph glands throughout the body that are connected by tiny vessels called lymph vessels.