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A to Z: Pilonidal Cyst

May also be called: Pilonidal Abscess; Pilonidal Sinus; Pilonidal Disease

A pilonidal (pie-luh-NIE-dul) cyst is a pocket (or pit) filled with hair and skin debris that usually forms in the skin near the end of the tailbone (coccyx) in the upper part of the cleft between the buttocks.

More to Know

Most doctors believe pilonidal cysts begin to form when a loose hair penetrates the skin and is forced deeper into the skin by friction and pressure from long periods of sitting, tight clothing, bicycling, or other causes. The body's immune system treats the hair as a foreign substance and forms a cyst around it that fills with fluid.


Pilonidal cysts may become infected and fill with pus. They can also penetrate deeper in the tissues and form a channel called a sinus tract. A pilonidal cyst might have no visible symptoms other than a small dimple in the skin. Cysts that become infected can be painful, tender, and swollen and may begin to drain fluid or blood.

Keep in Mind

If pilonidal cysts get infected, they can really hurt and should be treated. Treatment depends on how severe the cyst is, but can involve sitz baths, warm compresses, antibiotics, and a minor procedure to incise (lance and drain) the infected cyst, or surgery to clean out the cyst and sinus tract. Surgery is relatively simple, and a person typically heals completely within a few weeks. However, pilonidal cysts can recur (happen again).

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.

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