According to Fistula Treatment Experts, Fistula-in-Ano is an abnormal opening on the buttocks, other than the natural opening. 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.