Fistula (commonly anal fistula) is a chronic condition in which an abnormal tunnel forms between the anal canal and the skin near the anus. It usually develops after an infection or abscess that does not heal completely, leading to persistent discharge, pain, swelling, and irritation around the affected area.

Common symptoms include continuous or intermittent pus discharge, discomfort while sitting, pain during bowel movements, and sometimes bleeding. If left untreated, fistula can become more complicated and may lead to recurrent infections.