The anus is the opening of the digestive tract where bowel movements leave the body. An anal fissure is a tear or crack in the lining of the anus. An anal fistula is an abnormal opening in the skin near the anus.
Anal fissures are extremely painful.
Pain is often most severe during bowel movements. They can cause painful spasms of the muscles around the anus. Spots of bright red blood in the stool may be noticed. There is often a hemorrhoid-like thickening of the skin at the lower end of the fissure. The fear of pain during a bowel movement can cause constipation.