Anal fissures can be caused by trauma to the anus and anal canal. The trauma can be caused by one or more of the following:
- Chronic (long-term) constipation
- Straining to have a bowel movement, especially if the stool is large, hard and/or dry
- Prolonged diarrhea
- Anal sex, anal stretching
- Insertion of foreign objects into the anus
Causes other than trauma include:
- Longstanding poor bowel habits
- Overly tight or spastic anal sphincter muscles (muscles that control the closing of the anus)
- Scarring in the anorectal area
- An underlying medical problem, such as Crohn's disease and ulcerative colitis (types of inflammatory bowel disease); anal cancer; leukemia; infectious diseases (such as tuberculosis); and sexually transmitted diseases (such as syphilis, gonorrhea, Chlamydia, chancroid, HIV)
- Decreased blood flow to the anorectal area
Anal fissures are also common in young infants and in women after childbirth.