Cyst Symptoms and Causes

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A cyst is a closed sac-like structure that is not a normal part of the tissue where it is located. Cysts are common and can occur anywhere in the body in people of any age. Sometimes they may be felt as an abnormal or new lump or bump. Cysts usually are filled with air or other gases, liquids such as pus, or semisolid substances such as tissue debris or other materials. Since cysts vary in size, they may be detectable only under a microscope or they can grow so large that they displace normal organs and tissues. The outer wall of a cyst is called the capsule.

Cysts can arise through a variety of processes in the body, including

  • "wear and tear" or simple obstructions to the flow of fluid,
  • infections,
  • tumors,
  • chronic inflammatory conditions,
  • genetic (inherited) conditions, and
  • defects in developing organs in the embryo.

Sometimes you can feel a cyst yourself when you feel an abnormal "lump." For example, cysts of the skin or tissues beneath the skin are usually noticeable. Cysts in the mammary glands (breasts) also may be palpable (meaning that you can feel them when you examine the area with your fingers). Cysts of internal organs such as the kidneys or liver may not produce any symptoms or may not be detected by the affected individual. These cysts often are first discovered by imaging studies (X-ray, ultrasound, computerized tomography or CT scan, and magnetic resonance imaging or MRI).

There are hundreds of types of cysts that can arise in the body. Some of the more well-known types of cysts are:

  • epidermal inclusion cysts, small benign cysts of the skin;
  • cysts in the breast which are part of benign proliferative ("fibrocystic") disease (fibrocystic breast disease);
  • ovarian cysts;
  • cysts within the thyroid gland, or other organs such as the liver, kidneys, pancreas, testes, and ovaries;
  • Baker cyst (popliteal cyst) behind the knee;
  • ganglion cysts of the joints and tendons;
  • pilonidal cysts, cysts that occur on the skin near the cleft of the buttocks;
  • cysts that occur in the skin as part of acne (cystic acne);
  • cysts of the glands within the eyelid, termed chalazions, and;
  • sebaceous cysts of the small glands in the skin.

The majority of cysts are benign, but some may produce symptoms due to their size and/or location. Rarely, cysts can be associated with malignant tumors (cancers) or serious infections. If you're concerned about any abnormal swelling or "lump," talk to your doctor. He or she can recommend appropriate diagnostic tests to determine the cause of the cyst.


Fromm, L. J., et al. “Epidermal Inclusion Cyst.” Medscape. 6 June 2012.

Last Editorial Review: 3/13/2014