An anal fissure is a small split or tear in the thin moist tissue (mucosa) lining the lower rectum (anus). Anal fissures are very common in young infants. In adults, fissures may be caused by passing large, hard stools, or by having diarrhea for a long time. Anal fissures are also common in women after childbirth and in persons with Crohn’s disease.
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