What is a breast cyst?

A breast cyst is a noncancerous (benign), fluid-filled sac in the breast. It occurs when fluid fills an empty milk gland. Some cysts are too small to feel, while others grow up to several inches — large enough to make you uncomfortable. Clusters of cysts can form in one breast or both.

How common are breast cysts?

Breast cysts are common, especially for women in their later childbearing years. It’s easy to mistake them for a lump that could be cancer. About a quarter of breast masses turn out to be cysts.

Who gets breast cysts?

You’re more likely to get breast cysts if you are:

What causes breast cysts?

The exact cause of breast cysts is still unknown. Experts believe hormonal fluctuations may cause them to form. Breast cysts don’t usually develop in women after menopause, when estrogen levels taper off.

What are the symptoms of a breast cyst?

If you have a breast cyst, you may feel a lump that’s:

  • Soft or hard.
  • Round and smooth.
  • Painful, especially before your menstrual cycle.
  • Easily movable under the skin.

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