Anal Fissure - Causes

What are the causes of an anal fissure?

Anal fissures are most often caused by damage to the back passage (anus). Stretching and tearing of the rim of the anus can occur when a person passes particularly hard stools (faeces). In most people, this skin damage will heal quickly without any problems. However, some people seem to have a higher than normal tone (pressure) of the muscle around the anus (the anal sphincter). The muscle is 'tighter' than usual.

It is thought that this increased tone may reduce the blood supply to the anus and so slow down the skin healing process. This can cause an anal tear (fissure) to develop. Once a fissure has developed, pain when passing stools can increase the anal tone further. This makes the pain worse, which can then increase the muscle tone even more and further slow down the healing process.

Constipation can make an anal fissure more likely to develop. There's major variation in 'normal' frequency of bowel-opening between different people. For some, 2-3 times a day is standard and going three days without a bowel movement would be very unusual. For others, going more often than every 2-3 days would be equally odd. Constipation either happens if your stools become hard and it's harder and/or more painful to go, or you're going significantly less often than usual.

Lots of factors can cause constipation, but among the most common are not eating enough fibre (roughage) and not drinking enough fluids. If you're generally unwell, particularly with a feverish illness, you'll be losing more fluid than usual - due to sweating from your high temperature (fever) - and often eating less. Some medications - particularly strong painkillers - can also make you constipated. So can medical conditions such as an underactive thyroid gland.

Sometimes an anal fissure occurs if you have bad diarrhoea. Anal fissures are also more common during pregnancy and childbirth. An anal fissure occurs in about 1 in 10 women during childbirth.

In a small number of cases, a fissure occurs as part of another condition. For example, as a complication of Crohn's disease, ulcerative colitis or a sexually transmitted infection such as anal herpes infection. In these situations you will also have other symptoms and problems that are caused by the underlying condition. These types of fissures are not dealt with further in this leaflet.

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  • Anal Fissure; NICE CKS, July 2016 (UK access only)
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Author:
Dr Colin Tidy
Peer Reviewer:
Prof Cathy Jackson
Document ID:
4192 (v43)
Last Checked:
24 May 2017
Next Review:
23 May 2020

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. Patient Platform Limited has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.