Causes

Each of your breasts contains lobes of glandular tissue, arranged like petals of a daisy. The lobes are divided into smaller lobules that produce milk during pregnancy and breast-feeding. The supporting tissue that gives the breast its shape is made up of fatty tissue and fibrous connective tissue. Breast cysts develop as a result of fluid accumulation inside the glands in the breasts.

Breast cysts may be defined by their size:

• Microcysts may be seen during imaging tests, such as mammography or ultrasound, but are too small to feel.
• Macrocysts are large enough to be felt and can grow to about 1 to 2 inches (2.5 to 5 centimeters) in diameter.

Experts don't know exactly what causes breast cysts. They may develop as a result of hormonal changes from monthly menstruation.