A pilonidal sinus is a small hole or tunnel at the top of your bottom, between your buttocks. Treatment is usually only needed if it becomes infected.

Most people with a pilonidal sinus do not notice it unless it becomes infected and causes symptoms.

An infection will cause pain and swelling at the top of the cleft in your buttocks, and a pus-filled skin abscess can develop.

Sometimes a pus-filled abscess can develop suddenly, causing pain and swelling, and making it difficult to sit down.

If you keep getting infections you may have ongoing problems, like discomfort or pain, and regularly seeping pus or blood.

Ask for an urgent GP appointment or contact NHS 111 if:

Treatment is not needed for a pilonidal sinus 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.

Do not shave the affected area unless a GP advises you to.

Treatment for an infected pilonidal sinus will depend on:

• your symptoms
• the size of the pilonidal sinus
• whether it's your first infected pilonidal sinus or it keeps coming back

If you have a painful, swollen abscess, it usually needs to be cut and the pus drained. You may also need antibiotics.

There are a number of treatment options for a pilonidal sinus that keeps coming back and 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 non-steroidal anti-inflammatory drugs (NSAIDs), to help reduce pain and swelling.

Incision and drainage

This is a procedure for an infected abscess.

A small cut (hole) is made in the abscess so the pus can be drained. This is usually arranged on the same day as you see your GP.

• You'll have a local anaesthetic or general anaesthetic, depending on the size of the abscess.
• It will usually be done at a hospital (you can leave the same day) or can sometimes be done at your GP surgery.
• You may need a course of antibiotics.
• You'll need to have regular (daily) dressing changes.

Wide excision and open healing

You may need surgery for a large or repeatedly infected sinus.

The sinus is cut out and some surrounding skin removed. The wound is left open to heal naturally.

• You'll have a local anaesthetic or general anaesthetic.
• It will be done in hospital and you can usually leave the same day.
• You'll need to have regular dressing changes.
• This surgery gives you the lowest risk of a pilonidal sinus coming back.

Excision and wound closure

This surgery is for a large or repeatedly infected pilonidal sinus.

The sinus is removed and an oval-shaped flap of skin cut out on either side of it. The 2 sides are then stitched together.

• You'll have a local anaesthetic or general anaesthetic.
• It will be done in hospital and you can usually leave the same day.
• Your stitches will be removed about 10 days after the operation.
• This surgery gives you a quicker recovery time than wide excision and open healing.
• There is a higher risk of infection – the wound may need to be opened and dressings changed regularly.

Endoscopic ablation for a pilonidal sinus

This procedure is to clean a pilonidal sinus and encourage healing.

An endoscope (a thin, flexible tube with a camera on the end) is used to give a clear view of the affected area.

Hair and infected tissue are removed, and the sinus is cleaned with a special solution. Heat is used to seal the sinus.

• You'll have a spinal or local anaesthetic.
• It will be done in hospital and you can usually leave the same day.
• This procedure is less invasive than surgery as no cut is needed.
• It has a good success rate with a low risk of complications.
• The recovery time is about a month to completely heal, but it can be quicker.

Plastic surgery is sometimes used if the area being treated is particularly large. The sinus is removed and the surrounding skin reconstructed.

Less invasive procedures to close the sinus, like injection with fibrin glue, may be available in some places.

Follow-up

You may have a follow-up appointment with your specialist after your surgery. This is usually about 6 weeks later, but may be slightly longer.

Your care team will advise you about how to care for your wound while it heals and what to do if symptoms come back.

How soon you can return to work depends on:

• the procedure you had
• how quickly you recover
• the type of job you do

Most people are able to return to work within 2 weeks of surgery.

Your surgeon will be able to give you more advice about your recovery.

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.