A pilonidal (pie-low-NIE-dul) cyst is an abnormal pocket in the skin that usually contains hair and skin debris. A pilonidal cyst is almost always located near the tailbone at the top of the cleft of the buttocks.
Pilonidal cysts usually occur when hair punctures the skin and then becomes embedded. If a pilonidal cyst becomes infected, the resulting abscess is often extremely painful. The cyst can be drained through a small incision or removed surgically.
Pilonidal cysts most commonly occur in young men, and the problem has a tendency to recur. People who sit for prolonged periods of time, such as truck drivers, are at higher risk of developing a pilonidal cyst.
When it's infected, a pilonidal cyst becomes a swollen mass (abscess). Signs and symptoms of an infected pilonidal cyst include:
Reddening of the skin
Drainage of pus or blood from an opening in the skin
Foul smell from draining pus
When to see a doctor
If you notice any signs or symptoms of a pilonidal cyst, see your doctor. He or she can diagnose the condition by examining the lesion.
The exact cause of pilonidal cysts isn't clear. But most pilonidal cysts appear to be caused by loose hairs that penetrate the skin. Friction and pressure — skin rubbing against skin, tight clothing, bicycling, long periods of sitting or similar factors — force the hair down into skin. Responding to the hair as a foreign substance, the body creates a cyst around the hair.
This explanation accounts for rare cases of pilonidal cysts that occur in parts of the body other than near the tailbone. For example, barbers, dog groomers and sheep shearers have developed pilonidal cysts in the skin between fingers.
Certain factors can make you more susceptible to developing pilonidal cysts, such as:
Younger age (pilonidal cysts are most common in people in their 20s)
Occupation requiring prolonged sitting
Excess body hair
Stiff or coarse hair
If a chronically infected pilonidal cyst isn't treated properly, you may be at slightly increased risk of developing a type of skin cancer called squamous cell carcinoma.
To help prevent pilonidal cysts, try to:
Keep the area clean
Lose weight if needed
Avoid prolonged sitting
If you've had pilonidal cysts in the past, you might want to regularly shave the area or use hair removal products to reduce the risk of recurrence.