Irritable bowel syndrome (IBS) - Causes 

Causes of IBS 

The exact cause of irritable bowel syndrome (IBS) is unknown, but most experts agree it is related to an increased sensitivity of the entire gut.

This can be caused by:

  • a change in your body's ability to move food through your digestive system
  • becoming more sensitive to pain from your gut 
  • psychological factors
  • an episode of food poisoning

Digestion process

Your body usually moves food through your digestive system by squeezing and relaxing the muscles of the intestines in a rhythmic way.

However, in IBS it is thought this process is altered, resulting in food moving through your digestive system either too quickly or too slowly. Either way, there will be discomfort within the abdomen.

If food moves through your digestive system too quickly, you will have diarrhoea because your digestive system does not have enough time to absorb water from the food.

If food moves through your digestive system too slowly, you will have constipation because too much water is absorbed, making your stools hard and difficult to pass.

It may be that food does not pass through the digestive systems of people with IBS properly because the signals that travel back and forth from the brain to the gut, controlling the nerves, are disrupted in some way.

An increase in levels of a chemical called 5-hydroxytryptamine (5-HT), which can occur after eating certain foods or during times of stress, is also thought to affect the normal functioning of the gut.

Increased sensitivity

Many sensations in the body come from your digestive system. For example, nerves in your digestive system relay signals to your brain to let you know if you are hungry or full, or if you need to go to the toilet.

Some experts think that people with IBS may be oversensitive to the digestive nerve signals. This means mild indigestion that is barely noticeable in most people becomes distressing abdominal pain in those with IBS.

Psychological factors

There is a fair amount of evidence to suggest psychological factors play an important role in IBS.

However, this does not mean that IBS is "all in the mind", because symptoms are very real. Intense emotional states such as stress and anxiety can trigger chemical changes that interfere with the normal workings of the digestive system.

This does not just happen in people with IBS. Many people who have never had IBS before can have a sudden change in bowel habits when faced with a stressful situation, such as an important exam or job interview.

It has also been discovered that many people with IBS have experienced a traumatic event, usually during their childhood, such as abuse, neglect, a serious childhood illness or bereavement.

It is possible that these types of difficult experiences in your past may make you more sensitive to stress and the symptoms of pain and discomfort.

IBS triggers

Certain foods and drinks can trigger the symptoms of IBS. Triggers vary from person to person, but the most common ones include:

  • alcohol 
  • fizzy drinks
  • chocolate
  • drinks that contain caffeine, such as tea, coffee or cola
  • processed snacks, such as crisps and biscuits
  • fatty food
  • fried food

Keeping a food diary may be a useful way of identifying possible triggers in your diet.

Stress is another common trigger of IBS symptoms. Therefore, finding ways to manage stressful situations is an important part of treating IBS.

Read more about treating IBS.

Page last reviewed: 12/09/2012

Next review due: 12/09/2014

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