Anal fissure is a disease in which the surface of the narrowest part of the anal canal tissue, from the dentate line to the anal verge of the digestive tract, is cracked and does not heal repeatedly. The most common site for anal fissures is the front and back of the anus, with the front center being the most common. So, what are the causes of anal fissures? The following are the causes of anal fissures. A. Internal sphincter spasm The high tension of the internal sphincter can cause a significant increase in the resting pressure of the anal canal, so that the stretching of the anus is not enough, and when dry and hard stool is passed, a fissure will be produced. The internal sphincter is stimulated by fecal residue and intestinal fluid and spasms occur, resulting in severe pain. The main causes of increased tension of the internal anal sphincter are: 1. Exposure of the sphincter. 2, inflammation stimulates the internal sphincter muscle tension when inflammation occurs in the intestine, anal canal or anal sinus. 3, emotional abnormalities such as anger, tension. 4, acidic fecal stimulation as excessive stomach acid will stimulate the intestinal mucosa leading to gastric or duodenal ulcers, stomach cramps pain. Feces is generally alkaline, when the flora is out of balance feces becomes acidic, stimulating the internal sphincter of the anus to spasm. Second, ischemia When the anal fissure does not heal or recurring is called anal fissure, and local ischemia is the most important cause of anal fissure. There are two reasons for ischemia: 1. The blood vessel distribution supplies local blood to the anus from the anal artery, which is distributed from both sides to the middle and crosses in the front and back of the anus, resulting in two distribution weak zones in the front and back of the anus. 2, internal sphincter spasm anal canal tension is too high and blood circulation is poor. 3. Anatomical defects The external anal sphincter forms two triangular fissures in front and behind the anal canal, which lack sufficient support for the anal canal but can produce fissures when fecal impaction occurs. It is worth noting that the occurrence of anal fissures is caused by the accumulation of long-term, multiple etiologies, which include the reduction of the elasticity of the anal canal skin, impaired blood supply, easy damage to the anterior and posterior walls, reduced adaptability of the internal sphincter, anal injury, etc. 4. Abnormal stool The first reason for anal fissure is the impact or friction from external forces. If the stool is too coarse and hard, when the anal adaptation is poor, it will make the anal canal fissure. Some people found that not only constipation, diarrhea can also produce anal fissures, which can account for 4% to 7% of the causes of anal fissures.