Anal fistula 


An anal fistula is a small channel that develops between the end of the bowel, known as the anal canal or back passage, and the skin near the anus. The anus is the opening where waste leaves the body.

Some types of fistula have one channel, whereas others branch out into more than one opening. The fistula ends can appear as holes on the surface of the skin around the anus.

An anal fistula is painful and can cause bleeding when you go to the toilet.

Some fistulae can be connected to the sphincter muscles (the rings of muscles that open and close the anus).

When should I see my GP?

The common symptoms of an anal fistula include:

  • skin irritation around the anus
  • a throbbing, constant pain that may be worse when you sit down, move around, have a bowel movement or cough
  • a discharge of pus or blood when having a bowel movement 

You should see your GP if you have any of these symptoms. You may be referred to a specialist in bowel conditions, known as a colorectal surgeon, for further investigation.

Read more about diagnosing an anal fistula.

What causes an anal fistula?

An anal fistula usually develops after an anal abscess (a collection of pus) bursts, or when an abscess has not been completely treated. A fistula can also be caused by conditions that affect the intestines, such as Crohn's disease or ulcerative colitis.

As many as 50% of people with Crohn’s disease get an anal fistula. Up to 30% of people with HIV (a virus that attacks the body's immune system) will also develop an anal fistula.

Read more information about the causes of an anal fistula.

Anal fistulae are more common in men, mostly between the ages of 20 and 40. A study published in 2007 that looked at four different European countries, including England, found that there are between one and three cases of anal fistulae for every 10,000 people.

Treating an anal fistula

Most anal fistulae require surgery because they rarely heal if they are not treated. Several surgical methods are available, depending on where and how complicated the fistula is.

You may be able to go home on the day of surgery. However, if the fistula is difficult to treat you may need to stay in hospital for a few days. 

Read more information about treating an anal fistula and recovering from anal fistula surgery.

There is a risk of complications after anal fistula surgery, including:

For example, after the most common type of surgery for a fistula (known as a fistulotomy), the risk of an anal fistula coming back is around 21%. The risks vary depending on the type of procedure. You can discuss this with your surgeon.

Page last reviewed: 11/04/2012

Next review due: 11/04/2014


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Men's health 18-39

Health for men aged 18 to 39, including eating well, exercise, how to lose the gut and secrets of a sex doctor