An anal fistula is a small tunnel that develops between the end of the bowel and the skin near the anus (where poo leaves the body).
They’re usually the result of an infection near the anus causing 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.
- skin irritation around the anus
- a constant, throbbing pain that may be worse when you sit down, move around, poo or cough
- smelly discharge from near your anus
- passing pus or blood when you poo
- swelling and redness around your anus and a high temperature (fever) if you also have an abscess
- difficulty controlling bowel movements (bowel incontinence) in some cases
- Crohn’s disease (an inflammatory disease of the intestine)
- Radiation (treatment for cancer)
- Sexually transmitted diseases
- Diverticulitis (a disease in which small pouches form in the large intestine and become inflamed)