An anal fistula is a granulomatous canal that connects the anal canal or rectum to the perianal skin and consists of three parts: an internal opening, a fistula, and an external opening. The internal port is often located in the lower rectum or anal canal, and is mostly one; the external port is in the perianal skin, and can be one or more. It is characterized by long-lasting or intermittent recurrence and is mostly seen in young and middle-aged men. Etiology and clinical manifestations: Most fistulas are caused by perirectal abscesses, so the internal opening is mostly at the dentate sinus, and the external opening of the fistula spills a small amount of purulent, bloody, or mucus secretions, which can make the anus moist, itchy, and sometimes form eczema due to the stimulation of secretions. Treatment: Anal fistulas are difficult to heal on their own, and without treatment they can recur and form perirectal abscesses, so most patients need surgery.