Dry stool is a predisposing factor for anal fissures, not the underlying cause of anal fissures. Anal fissure is a deep and full fissure of the mucous membrane of the anal canal skin, resulting in a pyknotic ulcer. Most of them occur in the middle of the posterior wall of the anal canal, and a few in the middle of the anterior wall. The typical symptoms of anal fissures are anal pain during and after defecation, often accompanied by a small amount of bleeding. Anal fissure pain is characterized by a typical cyclic pain. There is a short interval of relief after defecation, about 5 minutes, and then the pain increases again due to the spasm of the dilator muscle, which can last for as long as 1 hour or even several hours, making the patient restless and very painful. The pain is repeated when defecating again, making the patient fearful of defecation and hold back the stool. Because of the pain, patients deliberately reduce the number of bowel movements and delay defecation, making the stool more constipated and aggravating the damage to the anal canal, forming a vicious circle: pain – sphincter spasm – hypertrophy – anal stenosis – delayed defecation – dry and hard stool – further fissure. Therefore, anal sphincter hypertrophy spasm anal canal stenosis is the cause of anal fissure.