Causes of IBS

What are the causes of IBS?

Alison Cullen
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An introduction to the causes of IBS

Irritable Bowel Syndrome (IBS) is a relatively common digestive complaint and can give rise to a wide variety of symptoms.

There is usually no single specific cause for the problem – each person can develop symptoms as a result of a range of different factors. These can include problems with the digestive system, psychological factors, increased gut sensitivity or adverse reactions to certain food types.

Finding out what is causing your symptoms is often the first important step in finding an effective treatment.


Your digestive system deals with all the food you consume and it is therefore logical that what you eat has an impact on your gut and subsequent IBS symptoms.

A broad range of foods can trigger symptoms in different people. Try using a food and symptoms diary to keep a record of what you eat and any adverse reactions you experience as a result. Some of the most common food triggers to look out for include:

  • Caffeine
  • Fatty or fried foods
  • Spices
  • Alcohol
  • Chocolate

Food intolerance can trigger IBS-like symptoms too. This digestive condition arises from a hypersensitivity to, or difficulty in digesting, certain food types. Common food intolerances include:

Click the links above to learn more about specific food intolerances.

Digestive system problems

The digestive tract is lined with muscle fibres that relax and contract in a process called peristalsis to allow the food you eat to be effectively transported through the stages of digestion. However, if food passes through the digestive system too quickly, gas, bloating and diarrhoea can occur.

On the other hand, if muscle contractions are too slow or weak, food will stay in the bowels longer than is necessary. This causes too much water to be reabsorbed into the body, leading to the formation of dry hard stools or constipation.

The speed at which the bowel moves food along its length is determined and coordinated by nerve signals in the digestive tract. With IBS, no physical abnormality in these nerve pathways can be found. This suggests that a change of sensitivity in the nerves of the brain-gut axis could lead to an interference with normal bowel function.

Gut sensitivity

It seems that some people simply have a more sensitive gut than others. The same experience may cause mild discomfort in one person yet give rise to significant pain in another.

Additionally, signals telling you that you need to go to the toilet are stronger in some people than others, which is why urgency is another common symptom of IBS.

Although the reasons for increased gut sensitivity of this nature are not clear, it is thought that an interference with the nerve signals from the brain to the gut can lead to an over-reaction of gut tissue when signals do eventually arrive. This exaggeration in nerve impulses may also work the opposite way, which could explain why psychological issues such as stress, anxiety or depression have been linked to IBS.

Psychological factors

As a physical abnormality in the gut cannot be found in IBS, psychological factors have also been greatly considered.

Although IBS is not a psychiatric disorder, it is believed that psychological factors can play a role.

Difficult experiences such as bereavement or abuse, even from many years before, can make you more susceptible to IBS. Such events can cause you to become more sensitive to stress and pain.

Stress is commonly found to affect symptoms of IBS. For example, sudden or stressful changes in your life such as moving house or a job interview can result in IBS symptoms in someone who does not normally experience the condition. Symptoms may ease once the stressful situation has passed.

If you are prone to anxiety or feel easily stressed, finding ways to manage your stress or anxiety will not only improve your general lifestyle and emotional wellbeing, but can also help to reduce symptoms of IBS.

IBS has also been linked to more serious cases of depression. Clinical depression must be addressed by a health professional and if anti-depressant medication is required, it has been known to also address IBS symptoms.


Women are twice as likely as men to be affected by IBS. This gives us cause to believe that hormones might play a role in causing IBS.

Fluctuating hormones can result in many symptoms, and women have reported a worsening of IBS at certain points in their menstrual cycle. Some go as far as to describe IBS symptoms as part of pre-menstrual syndrome (PMS). The same can be said for women going through the menopause.

It is interesting to note that the female hormone progesterone has been found to decrease motility of the gut. When the levels of this hormone change (both independently and relative to the hormone oestrogen) for example around the time of a woman’s period, and during the menopause, IBS symptoms are likely to worsen. Constipation in particular is a likely outcome.

Gut bacteria

The human gut is home to billions of bacteria. These bacteria, or microbiota, can be beneficial to us when residing in the correct proportions.  Dysbiosis is the term used when an imbalance of your gut bacteria occurs.

If the benefits of the friendly bacteria in your gut are surpassed by the effects of the bad bacteria, you are likely to experience unpleasant symptoms such as bloating, flatulence, cramps, constipation or diarrhoea.

The beneficial effects of your good gut bacteria are also thought to have effects on other areas of the body, including the immune system and weight management, so your health may suffer in other ways if dysbiosis occurs.


A genetic link with IBS has long been disputed.

However, research suggests that a particular genetic defect can result in symptoms. Genes concerned with metabolism and serotonin synthesis are now thought to play a role in causing IBS.

Kumar, S. et al (2012) Serotonin transporter gene (SLC6A4) polymorphism in patients with irritable bowel syndrome and healthy controls. J Gastrointestin Liver Dis 21(1): 31-38

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