Pilonidal sinus

A pilonidal sinus is a small hole or tunnel in the skin at the top of the buttocks, where they divide (the cleft). It doesn't always cause symptoms and only needs to be treated if it becomes infected.

Check if you have an infected pilonidal sinus

Most people with a pilonidal sinus don't notice it unless it becomes infected and causes symptoms.

An infection will cause pain and swelling, and a pus-filled abscess can develop.

See a GP if:

• you have a small lump at the top of your bottom (between your buttocks) that's painful, red, bleeding or leaking pus

These symptoms can develop quickly, often over a few days. They're signs of infection and need treating.

A pilonidal sinus that isn't infected

Treatment isn't needed if there are no signs of infection. A "watch and wait" approach will be recommended.

It's very important to keep the area between your buttocks clean by showering or bathing regularly. Don't shave the affected area unless your GP advises you to.

Treatments for an infected pilonidal sinus

Treatment for an infected pilonidal sinus will depend on:

• your symptoms
• the size of the sinus
• whether it's your first sinus or a recurring problem

A pilonidal sinus abscess will need treatment with antibiotics. The pus inside will also probably need to be drained.

There are a number of treatment options for a recurring pilonidal sinus that's painful, bleeding or leaking discharge. Your doctor will discuss these with you.

In most cases you'll be offered painkillers, such as paracetamol and anti-inflammatories to help reduce pain and swelling.

What to do after your operation

Causes of pilonidal sinus

It's not clear what causes a pilonidal sinus.

A skin problem, pressure or friction may cause hair between the buttocks to be pushed inwards.

This may either be hair growing around the buttock area, or loose hair shed from the buttocks or elsewhere that gathers around the buttock cleft and enters the pilonidal sinus.

Pilonidal sinuses are more common in men because they tend to be hairier.

Sitting for long periods can also increase your chances of getting a pilonidal sinus.