Cracks on the side of the anus may be due to anal fissure, anal eczema, dermatitis and so on. 1. anal fissure: anal fissure, may be due to anal fissure, this disease is due to the anal canal skin longitudinal dehiscence, resulting in small localized ulcers. This disease will cause the patient to appear blood in the stool, pain and itching, constipation and other symptoms. 2. Anal eczema: the cause of anal eczema is not clear, this is a chronic skin disease with recurrence, will cause the patient around the anus pimples, small blisters, accompanied by severe itching, when the blisters burst, will cause the skin around the anus cracks. 3. Dermatitis: perianal dermatitis can also cause the anal side of the skin fissure symptoms, in the early stages of the disease will cause severe local itching, pimples, with the development of the disease will cause the local skin thickening, dryness, roughness, the formation of fissures. Once the fissure on the anal side is found, it should be timely to the hospital examination, for the cause of the treatment, follow the doctor’s instructions.