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Symptoms of 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 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:
- you have a small lump at the top of your bottom (between your buttocks) that's painful, 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 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.
Treatments for an infected pilonidal sinus
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.
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.
Pilonidal sinus
Pilonidal sinus
Pilonidal sinus
An infected pilonidal sinus is painful and swollen and may bleed or leak pus.
An infected pilonidal sinus usually needs to be cut and the pus drained. In some cases, you may need antibiotics or surgery.
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.
Content supplied by the NHS website, refreshed 19 August 2026. View the original NHS article ↗
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