An anal fistula is an infected canal that connects the rectum to the skin around the anus and generally consists of three parts: a primary internal opening, a fistula, and a secondary external opening. The main symptom is the repeated outflow of pus or pus and blood from the sore in the skin around the anus. Anal fistula generally refers to anorectal fistula, which is known as hemorrhoid leakage in traditional Chinese medicine and is a common anal disease. An anal fistula is a granulomatous tube that connects the anal canal or rectum to the perianal skin, mainly invading the anal canal and rarely involving the rectum, so it is often called an anal fistula. The entire fistula wall is composed of thickened fibrous tissue with a layer of granulation tissue that does not heal over time. It is second only to hemorrhoids in incidence and is most often seen in young male adults, probably due to the high secretion of sebaceous glands, one of the male sex hormone target organs. Most anal fistulas are nonspecific infections, and a few are tuberculous. The main symptoms are perianal or gluteal fistulae that do not heal over time, or fester at times, spilling pus and irritating the local skin with itching and discomfort. Anal fistulas do not heal on their own, and without treatment they can recur as perirectal abscesses, so they must be treated surgically.