A small fissure inside the anus is generally considered to be the development of an anal fissure, and the etiology can be related to a variety of factors or diseases. Anal fissure refers to the small ulcers that appear when the skin layer of the anal canal below the dentate line is cracked, mostly occurring in the anterior midline, with symptoms of severe pain in the perianal area. Anal fissure mostly in long-term constipation, fecal dryness, hard defecation caused by mechanical injury to the perianal skin, in addition, diarrhea can also lead to anal fissure. If there is an anal fissure on the side of the anus, it can be considered to be caused by ulcerative colitis, Crohn’s disease, intestinal tuberculosis, perianal tumors and other causes of perianal ulcers. In anal fissure, there will be periodic pain in defecation, and fresh blood can be seen on the surface of the stool paper or feces. When you find perianal fissures and feel pain in the perianal area, it is recommended that you seek medical attention in time to clarify the cause of the disease and then treat the symptoms to avoid aggravation of the condition.