what causes pilonidal cysts
A pilonidal cyst is a small sac under the skin. Pilonidal cysts may become infected and cause an abscess (collection of pus). Pilonidal cysts may be caused by an ingrown hair. A hair may become ingrown if it rubs against your skin. The friction can cause hair to dig into the skin and get trapped there. A pilonidal cyst may look like a small hole or dimple in the center of your lower back. It is usually located right above your buttocks.