A pit, often containing hairs, at the top of the cleft between the buttocks
A pilonidal sinus is a small, enclosed pit beneath the skin at the top of the cleft between the buttocks. The condition occurs most commonly in men with a lot of body hair. The exact cause is unknown but may be a defect in the development of that area. Hair growth at the site tends to be directed inwards, which may cause infection in the sinus and result in a painful abscess.
Prompt action at the first signs of infection may prevent an abscess from forming. You should soak the area in warm water to relieve discomfort and consult your doctor as soon as possible. You may be prescribed oral antibiotics to treat the infection. If pus has built up, the abscess will need to be drained under general anaesthesia and left open to heal. In most cases, the infection is unlikely to recur.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.