Embarrassing Illnesses

The cause of your anal fissure will depend on whether it is a primary or secondary fissure.

Primary anal fissures

This type of anal fissure is not caused by an underlying condition. However, it is thought to be associated with the way the muscles in your anus work.

The muscle which surrounds the anus (known as the internal sphincter) can sometimes contract too strongly (spasms). This causes increased pressure in the anal canal, making it more susceptible to tearing. The increased pressure also restricts the blood flow to your anus. Reduced blood flow stops your body from being able to heal itself as well as normal, which means that it will be difficult for your fissure to heal naturally.

Secondary anal fissures

A secondary anal fissure is caused by an underlying condition. The conditions which can cause an anal fissure are outlined below.

Constipation

Constipation is the most common cause of a secondary anal fissure. Constipation is a very common condition which means that you are not passing stools as regularly as you normally do. This can cause your stools to become dry and hard.

Passing a hard stool can sometimes tear the lining of the anus. Avoiding passing stools because of the pain of an anal fissure will often worsen your constipation, which means that your fissure will not have a chance to heal.

Inflammatory bowel disease (IBD)

Inflammatory bowel disease (IBD) is a term that is used to refer to a number of conditions which cause inflammation in the intestines, such as Crohn's disease and ulcerative colitis.

IBD can sometimes cause ulcers to form on the lining of the anus, which can lead to an anal fissure developing.

Sexually transmitted infection (STI)

If the lining of the anus becomes infected with an STI, it can cause the tissue to break down, resulting in an anal fissure.

Pregnancy

During the third trimester of pregnancy (week 29 to birth), your risk of having an anal fissure is increased. You may also develop an anal fissure during childbirth because the continual straining of your muscles can sometimes cause the lining of your anus to tear.

Cancer of the rectum

In very rare cases, an anal fissure can be a sign of cancer. Your GP will know if your fissure is a sign of a more serious illness from your other symptoms, and the appearance of your fissure. They will then be able to immediately refer you for further testing if they think it is necessary. However, it is important to remember that in the majority of cases, an anal fissure will not be caused by cancer. 

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