An anal fistula is a fistula around the anal canal and rectum that is connected to the anal canal or rectum at one end and to the skin around the anal canal at the other end. It usually consists of three parts: the primary internal opening, the fistula and the secondary external opening. It is mostly seen in male young adults and male infants. The fistula is intermittent or persistent and does not close for a long time. If the pus is too tired, the pus will increase and sometimes feces may flow out; if the pus is already small but suddenly increases and there is pain in the anus, it often indicates an acute infection or the formation of a new branch. 2. Pain When the fistula is open, there is usually no pain, but only a local feeling of swelling. If the external opening closes on its own and pus accumulates, local pain may occur or there may be chills and fever; if the pus flows out after the fistula breaks, the symptoms may be rapidly reduced or disappear. However, pain can also be caused by the large inner mouth and the inflow of feces into the duct, especially when the pain increases during defecation. 3.Itching Itching is caused by pus constantly stimulating the skin around the anus, and sometimes it can be accompanied by perianal eczema.