The exact cause of IBS is unknown, although most experts agree that it's related to a disruption in the normal process of digestion.
This can be due to:
- a change in your body's ability to move food through your digestive system
- you becoming more sensitive to pain from your gut
- psychological factors
Food movement through the gut
Normally, your body moves food through your digestive system by squeezing then relaxing the muscles of the intestines in a rhythmic way.
If you have IBS, it's thought this process is disrupted, so food moves through your digestive system too quickly or too slowly. Moving too quickly results in diarrhoea because your digestive system does not have enough time to absorb water from the food. If food moves too slowly, the result is constipation, because too much water is absorbed, which makes stools hard and difficult to pass.
Theories suggest that, in people with IBS, food doesn't pass through the digestive system properly because the signals that travel back and forth from the brain to the gut, controlling the muscles, are disrupted in some way.
An increase in levels of the chemical 5-hydroxytryptamine (5-HT) which can happen after eating certain foods or during times of stress is also thought to affect the normal process of the digestive system.
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 believe that if you have IBS you are oversensitive to these digestive nerve signals so mild indigestion that is barely noticeable in most people becomes distressing abdominal pain.
Psychological factors
There's a lot of evidence that psychological factors play an important role in IBS.
This doesn't mean that IBS is "all in the mind" – the symptoms are very real. But intense emotional states, such as stress and anxiety, can trigger chemical changes that interfere with the normal workings of the digestive system.
This doesn't just happen in people with IBS. Many people who have never had IBS can have a sudden change in bowel habits when faced with a stressful situation, such as an important exam or a job interview.
It's also been found 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 difficult experiences in your past, such as these, make you more sensitive to stress and the symptoms of pain and discomfort.
IBS triggers
Certain foods and drinks can trigger IBS symptoms. 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.
Another common trigger of IBS symptoms is stress. So, finding ways to cope better with stressful situations is an important part of treating IBS.
Read more about treating IBS.
