An anal fissure is a crack or slit in the mucous membrane of the anus.

If you feel pain during defecation or see blood in your stool, you may have an anal fissure. Fissures sometimes are mistaken for hemorrhoids because both can cause bleeding.

A hard, dry bowel movement can cause a fissure. Other causes include diarrhea or inflammatory conditions of the anal area. Anal fissures may be acute (recent onset) or chronic (present for a long time or recurring frequently). A small external lump called a sentinel pile or skin tag may form near the fissure.

Several treatments exist for treating anal fissures and may not require an operation.