Anal fissure is a common anal disease, anal fissure is a small ulcer in the skin layer of the anal canal below the dentate line, mostly occurs in middle-aged people, often causing severe pain and healing difficulties, bringing pain to patients, so what exactly is the cause of anal fissure, the following take a look. 1, infection Acute and chronic anal sinusitis, anal papillitis, internal hemorrhoids and polyps are the main causes of infection. The pathogenic bacteria of the infection enter the anal gland through the glandular opening and generate abscesses in the subcutaneous tissue of the anal canal, which form ulcers after breaking down. Small superficial thrombosis occurs due to infection, which can also lead to anal fissure. 2, constipation Constipation is the main cause of anal fissure, due to the weakening of intestinal contraction movement, so that the movement of feces from the cecum to the rectum slowed, or due to the uncoordinated movement of the left hemicolectomy caused by constipation, feces long stay in people’s intestines, the texture of dry and hard, difficult to discharge, when the discharge will struggle, long-term constipation is easy to form anal fissures, fissures occur after defecation will produce severe pain. Patients will be afraid of defecation, often appear to hold back the stool, stool is not discharged in time, and will cause constipation, constipation will aggravate the fissure, fissure will aggravate constipation, and so on vicious circle. 3, injury dry stool can make the anal skin tear, diarrhea, frequent defecation makes the anal canal sensitive tight, the normal consistency of stool can also cause injury, chronic inflammation of the anal canal, fibrous tissue proliferation, the formation of anal comb hard knots, preventing the sphincter relaxation, so that the anal canal is vulnerable to injury rupture. Rectal foreign bodies, improper anal dilation methods, anal surgery, childbirth, congenital anal stenosis, proctocolitis, tuberculosis, etc. can also lead to anal fissures.