A tear in the lining of the anus that is usually a result of constipation
The most common cause of an anal fissure is the passage of a large, hard stool due to constipation. This type of stool can tear the anal lining so that subsequent defecation is extremely painful. You may also notice bright red blood on your faeces or the toilet paper.
An anal fissure can usually be diagnosed from a description of the symptoms, although in some cases the doctor may inspect the anal lining using a viewing instrument called a proctoscope.
Self-help measures to relieve constipation, such as using laxatives and eating a high-fibre diet, may help the anal fissure to heal. In addition, a gel that relaxes the anal sphincter (the ring of muscle around the anus) or an anaesthetic gel may be helpful. In severe cases, surgery to stretch or cut the anal sphincter may be recommended.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.