Anal fistula

An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the opening of the bottom (anus).

It’s usually caused by an infection near the anus, which results in a collection of pus (abscess) in the nearby tissue.

When the pus drains away, it can leave a small channel behind.

Anal fistulas can cause unpleasant symptoms, such as discomfort and skin irritation, and will not usually get better on their own.

Surgery is recommended in most cases.

Symptoms of an anal fistula

Symptoms of an anal fistula include:

The end of the fistula might be visible as a hole in the skin near your anus, although this may be difficult for you to see yourself.

When to get medical advice

See a GP if you have persistent symptoms of an anal fistula. They'll ask about your symptoms and whether you have any bowel conditions.

They may also ask to examine your anus and gently insert a finger inside it (rectal examination) to check for signs of a fistula.

If the GP thinks you might have a fistula, they can refer you to a specialist called a colorectal surgeon for further tests to confirm the diagnosis and determine the most suitable treatment.

Tests you may have include:

When to get medical help

The GP will look at the skin around the opening of your bottom (anus) to check for signs of an anal fistula.

They may also ask you if they can do a rectal examination. This involves gently inserting a gloved finger into your bottom.

If the GP thinks you have an anal fistula, you may be referred to a specialist for further tests.

Tests you may have include:

Causes of anal fistulas

Most anal fistulas develop after an anal abscess. You can get one if the abscess does not heal properly after the pus has drained away.

Less common causes of anal fistulas include:

Treatments for an anal fistula

Anal fistulas usually require surgery as they rarely heal if left untreated.

The main options include:

All the procedures have different benefits and risks. You can discuss this with the surgeon.

Many people do not need to stay in hospital overnight after surgery, although some may need to stay in hospital for a few days.

Find out more about treating an anal fistula

Page last reviewed: 21 February 2023
Next review due: 21 February 2026