An anal fissure is a small tear in a thin, moist tissue (mucosa) that is arranged in the anus. Anal fissure can occur when you pass hard or loose stools during defecation. Anal fissures often cause pain and bleeding in bowel movements. You may also have sputum in the muscle ring at the end of the anus (anal sphincter). Anal fissures are common in young children but can affect people of any age.