An anal fissure is a small tear in the lining of your bottom (anus).
Symptoms of an anal fissure include a sharp pain and bleeding when you poo.
Anal fissures are usually caused by constipation. Other causes include long-lasting diarrhoea, inflammatory bowel disease, pregnancy and childbirth.
An anal fissure usually heals on its own. Treatment includes avoiding constipation, and medicines to reduce pain and speed up healing.