A pilonidal cyst may look like a small hole or dimple under the skin at the top of the crease of the buttocks. Pilonidal cysts usually do not cause problems unless they become infected.

The exact cause of a pilonidal cyst isn't clear. It may start when loose hair and other skin debris get trapped in an enlarged skin pore, creating a cyst. If the cyst (also called a pit or sinus) gets infected, it can form an abscess.

Symptoms of an infected pilonidal cyst include:

• Pain.
• Swelling and redness.
• Drainage of pus and/or blood.
• Fever.

A pilonidal cyst can develop a long-lasting or frequently recurring infection. Treatment includes medicines, draining an abscess, or surgery to remove the cyst.