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Causes
By Mayo Clinic staffEach of your breasts contains 15 to 20 lobes of glandular tissue, arranged like the petals of a daisy. The lobes are further divided into smaller lobules that produce milk during pregnancy and breast-feeding. Small ducts conduct the milk to a reservoir just beneath your nipple. Supporting this network is a deeper layer of connective tissue called stroma.
Breast cysts develop when an overgrowth of glands and connective tissue (fibrocystic changes) block milk ducts, causing them to dilate and fill with fluid.
- Microcysts are too small to feel but may be seen during imaging tests, such as mammography or ultrasound.
- Macrocysts are large enough to be felt and can grow to about 1 to 2 inches (2.5 to 5 centimeters) in diameter. Large breast cysts can put pressure on nearby breast tissue, causing breast pain or discomfort.
The cause of breast cysts remains unknown. Some evidence suggests that excess estrogen in your body may play a role in breast cyst development.
