What causes irritable bowel syndrome?
Exactly what causes irritable bowel syndrome (IBS) isn't known. It may have something to do with overactivity of part or parts of the gut (bowel). Food is passed along the bowel by regular squeezes (contractions) of the muscles in the wall of the bowel wall. Pain and other symptoms may develop if the contractions become abnormal or overactive. The area of overactivity in the gut may determine exactly where you feel the pain and whether constipation or diarrhoea develops.
The cause of overactivity in parts of the gut is not clear. One or more of the following may play a part:
- Overactivity of the nerves or muscles of the gut. It is not known why this may occur. It may have something to do with overactivity of messages sent from the brain to the gut. Stress or emotional upset may play a role. About half of people with IBS can relate the start of symptoms to a stressful event in their lives. Symptoms tend to become worse during times of stress or anxiety.
- Intolerance to certain foods may play a part in some cases. However, this is thought to be only in a small number of cases.
- Infection and germs (bacteria) in the gut. IBS is not caused by an ongoing gut infection. However, in some cases, the onset of symptoms seems to follow a bout of a gut infection with diarrhoea and being sick (vomiting), called gastroenteritis. So, perhaps a virus or other germ may sensitise or trigger the gut in some way to cause persisting symptoms of IBS.
- Oversensitivity to pain. People with IBS feel more pain when their gut is expanded (dilated) than those without IBS. They may have a lower threshold for experiencing pain from the gut.
Further reading and references
Irritable bowel syndrome in adults: diagnosis and management of irritable bowel syndrome in primary care; NICE Clinical Guideline (February 2008, updated April 2017)
Irritable bowel syndrome; NICE CKS, February 2013 (UK access only)
Ruepert L, Quartero AO, de Wit NJ, et al; Bulking agents, antispasmodics and antidepressants for the treatment of irritable bowel syndrome. Cochrane Database Syst Rev. 2011 Aug 10(8):CD003460.
Bohn L, Storsrud S, Liljebo T, et al; Diet low in FODMAPs reduces symptoms of irritable bowel syndrome as well as traditional dietary advice: a randomized controlled trial. Gastroenterology. 2015 Nov149(6):1399-1407.e2. doi: 10.1053/j.gastro.2015.07.054. Epub 2015 Aug 5.
Didari T, Mozaffari S, Nikfar S, et al; Effectiveness of probiotics in irritable bowel syndrome: Updated systematic review with meta-analysis. World J Gastroenterol. 2015 Mar 1421(10):3072-84. doi: 10.3748/wjg.v21.i10.3072.
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