An anal fissure is a common and often painful problem caused by a small tear or ulcer open sore in the lining of the anus back passage. This can cause bleeding, local itching and pain with a bowel movement, which can be severe. When someone has an anal fissure the first treatments can include a high-fibre diet, laxatives and applying anaesthetic ointments to the affected area. Anal fissures usually heal within a few weeks but those that have not healed after 4—6 weeks are called chronic fissures. If someone has a chronic fissure, it is thought that the reason it has not healed is that the ring muscle sphincter that goes around the anus back passage has become so tense that the flow of blood to the lining of the anus is reduced. That means that not enough oxygen carried by the blood gets to the fissure or tear.