An anal fissure is a tear in the lining of the anus or anal canal the opening through which stool passes out of the body. The fissure can be painful and may bleed. Anal fissures can occur in anyone at any age. The chance of having an anal fissure decreases as people get older. People who have had fissures in the past are more likely to have them in the future. Anal fissures can be caused by trauma to the anus and anal canal.