An anal fissure is a tear in the lining of the lower rectum anal canal that causes pain during bowel movements. Anal fissures don't lead to more serious problems. Most anal fissures heal with home treatment after a few days or weeks. These are called short-term acute anal fissures. If you have an anal fissure that hasn't healed after 8 to 12 weeks, it is considered a long-term chronic fissure. A chronic fissure may need medical treatment.