A pilonidal sinus is a small hole or tunnel in the skin, usually at the top of the cleft between the buttocks. In some people dents(small depressions) in the skin develop naturally in this area.Pilonidal sinuses form in these dents in the skin, often around a hair follice – the tiny holes in the skin that hairs grow out of. Doctors are not sure what causes a pilonidal sinus, but it may be caused by ingrown hairs, or when the dents in the skin get blocked with bits of hair and skin. Pressure or friction to the skin may also be a factor. The sinus can then become infected.

Who gets pilonidal sinuses?

Pilonidal sinuses are most common in young adults and are rarely seen in children or people over 40 years old. They happen slightly more often in men than women and seem to occur more often in people with a lot of body hair.

Certain factors increase the risk of developing a pilonidal sinus including:

1. spending lots of time sitting down
2. obesity
3. a previous injury to the skin
4. frequent irritation of the skin
5. a family history of the condition.

Symptoms

If the pilonidal sinus becomes infected, this will cause pain and swelling, and an abscess full of pus will develop. This can happen quite quickly, over a few days. It can also be a long-term problem that keeps coming back.

Treatment

If you have no symptoms then you will normally be advised to shave the affected area, to keep the area clean, and to dry well after washing.