Pilonidal sinus is a skin condition that causes infected and ingrown hairs around the crease of the buttocks, usually leading to a cyst or abscess.

Once the abscess heals, either on its own or with treatment, a pilonidal sinus may develop. The sinus is like a pipe just under the skin with tiny openings to the surface of the skin.

A pilonidal sinus is a small hole or tunnel in the skin that can easily become infected. It typically forms in the cleft at ...