A pilonidal cyst is a small pit, or dimpled area, that can occur anywhere along the crease between the buttocks (sacral area).

Most pilonidal cysts are pits or small depressions that are present from birth. They may range from a small dimple to a deep tract with hair in or around it.There may be more than one pit present. Very rarely, the pilonidal cyst may reach the spinal cord.

A pilonidal cyst may become infected, forming what is called a pilonidal abscess. This may require surgical drainage. If repeated infection occurs, surgery may be done to remove it.

The cause of pilonidal cysts is not certain. These cysts may be congenital (present from birth). In some cases, they might be caused by hair growing into the skin. This may occur with excess body hair, tight clothing, or sitting for long periods of time.