Incontinence, bowel - Causes 

There are three main factors that can affect normal bowel function and cause bowel incontinence.

These are:

• Problems with the rectum: the rectum (where stools are held) is unable to store stools properly until it is time to go to the toilet.
• Problems with the sphincter muscles: the muscles at the top and bottom of the rectum do not work properly.
• Nerve damage: the nerve signals sent from the rectum do not reach the brain.

These problems are each explained in more detail below.

Problems with the rectum

Constipation

Constipation is a leading cause of bowel incontinence.

In cases of severe constipation, a large, solid stool can become stuck in the rectum. This is known as faecal impaction. The stool then begins to stretch the muscles of the rectum, weakening them.

Watery stools can then leak around the stool and out of the bottom, causing bowel incontinence.

Diarrhoea

It is more difficult for the rectum to hold liquid stools (diarrhoea) than solid stools, so people with diarrhoea (particularly recurring diarrhoea) can develop bowel incontinence.

Conditions that can cause recurring diarrhoea include:

• Crohn's disease - a condition that causes inflammation of the digestive system
• irritable bowel syndrome - a condition that causes a range of digestive symptoms, such as diarrhoea and bloating
• ulcerative colitis - a condition that causes inflammation of the large bowel

These three conditions can also cause scarring of the rectum, which can lead to bowel incontinence.

Rectal cancer

Cancerous tumours that develop inside the rectum can sometimes cause bowel incontinence.

Problems with the sphincter muscles

The sphincter muscles at the top and bottom of the rectum act like gates, opening and closing as necessary.

You do not have control of the internal sphincter (at the top), which opens automatically to let stools pass into your rectum.

Once your rectum is full, nerve endings in your rectum send a signal to your brain to ‘tell’ you that you need to pass a stool.

You normally have control over your external sphincter (at the bottom), so this stays closed until you find a convenient time to go to the toilet, at which point your external sphincter will open and stools will pass out.

Childbirth

Childbirth is one of the most common causes of damage to the sphincter muscles and a leading cause of bowel incontinence.

During a vaginal delivery of a baby, the sphincter muscles can become stretched and damaged, particularly as a result of a forceps delivery.

Other causes

Sphincter muscles can also become damaged through injury, or damage that arises as a complication of bowel or rectal surgery.

Nerve damage

A number of conditions can damage the nerves that connect the rectum to the brain, causing bowel incontinence. These conditions include:

• diabetes 
• multiple sclerosis (a condition of the central nervous system)
• stroke 
• spina bifida (a series of birth defects that affect the development of the spine and nervous system)

Any injury to the nervous system, such as spinal injury, can also lead to bowel incontinence.

Complete loss of bowel control

In a number of other health conditions, there is no physical damage but a person loses their ability to control their bowel properly.

These conditions include:

• Alzheimer’s disease 
• other forms of dementia
• severe learning disabilities