A pilonidal sinus is a small hole or tunnel in the skin at the top of the buttocks, where they divide (the cleft). It does not 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 do not notice it unless it becomes infected and causes symptoms.
An infection will cause pain and swelling and a pus-filled abscess can develop.
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 be hair growing around the buttock area. it could also be 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.
When to contact your GP
Contact your 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 to be treated.
A pilonidal sinus that's not infected
Treatment is not needed if there are no signs of infection. A 'watch and wait' approach is 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 your GP tells you to.
Treatment 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 it keeps coming back
A pilonidal sinus abscess will need treatment with antibiotics. The pus inside will also probably need to be drained.
You'll need treatment if you have a pilonidal sinus that keeps coming back if it is painful, bleeding or leaking discharge. Talk to your GP about treatment options.
In most cases you'll be offered painkillers to help reduce pain and swelling.
Minor operation to drain pus from sinus
Incision and drainage
If this is your first pilonidal sinus abscess, you may need to get it drained in hospital. A small hole is made in the abscess so the pus can be drained. You will need to have a general anaesthetic or local anaesthetic, depending on the size of the abscess. You will not usually need to stay in hospital overnight.
Your recovery time is usually between 4 to 6 weeks and you'll need to have regular dressing changes.
Surgery to remove sinus (wound left open)
Wide excision and open healing
You will need to have surgery for a large or repeatedly infected sinus. You will have a general anaesthetic (you'll be asleep) during this operation. The sinus is cut out and some surrounding skin removed. The wound is left open to heal naturally. You will not usually need to stay in hospital overnight.
Your recovery time is usually between 6 to 12 weeks. You'll need to have regular dressing changes.
There is a low risk of the sinus coming back.
Surgery to remove sinus (wound closed)
Excision and wound closure, often with flattening of the groove between the buttocks
You will need to have surgery for a large or repeatedly infected sinus. You will have a general anaesthetic (you'll be asleep) during this operation. The sinus is removed and an oval-shaped flap of skin cut out on either side of it. The 2 sides are stitched together. The stitches are removed about 10 days after the operation. You will not usually need to stay in hospital overnight.
There is a high risk of infection so the wound may need to be opened and dressings changed regularly.
Procedure to clean sinus and encourage healing
Endoscopic ablation for a pilonidal sinus
An endoscope (a thin, flexible tube with a camera on the end) is used to give a clear view of the affected area. You will have a spinal or local anaesthetic (you'll be awake) for this procedure.
Hair and infected tissue are removed, and the sinus cleaned with a special solution. Heat is used to seal the sinus. You will not usually need to stay in hospital overnight.
This procedure is less invasive than surgery as no cut is needed.
Plastic surgery is sometimes used if the area being treated is particularly large. The sinus is removed and the surrounding skin reconstructed.
You'll have a follow-up appointment with your specialist after your surgery. This is usually about 6 weeks later, but may be slightly longer.
What to do after your operation
keep the affected area clean
wear comfortable, loose-fitting cotton underwear
eat plenty of fibre to make going to the toilet easier and avoid straining
do not lift heavy objects or do strenuous exercise for the first week or so
do not ride a bike for 6 to 8 weeks
do not go swimming until your wound has completely healed
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 can return to work within 2 weeks of surgery.
Your surgeon will give you more advice about your recovery.
Content supplied by the NHS and adapted for Ireland by the HSE