A pilonoidal sinus is an infected tract which commonly contains hairs. It occurs under the skin between the buttocks (the natal cleft) a short distance above the back passage (anus). The tract may discharge pus from time to time on to the skin. There are a variety of treatments for pilonoidal sinus depending on the severity of the condition.

Treatments include clearing the affected area of hairs (by shaving, etc) and to keep the area clean with good personal hygiene; using antibiotics for infections or, for persistant symptoms, surgery is advised which usually entails excision of the area and coverage with a skin flap.