Anal fissures are common in infants but less so in older children. They occur in adults of all ages. The pain, which can be quite severe, usually occurs during and after a bowel movement. The most common cause of anal fissures is constipation, but diarrhea can be a cause as well. Anal fissures often result from a cycle in which you have pain as a result of constipation, avoid having a bowel movement, and thus worsen the constipation. Treatment involves changing your diet to eliminate diarrhea or constipation, or topical medications to help heal the tear. However, some people need surgery to treat an anal fissure. Anal fissures are not associated with cancer, but you should always talk to your doctor if you have bleeding with a bowel movement.