Diarrhoea - Causes 

Causes of diarrhoea 

Media last reviewed: 11/03/2013

Next review due: 11/03/2015

How diarrhoea occurs

Faeces can become watery for any of the following reasons:

  • the lining of the digestive system is damaged by bacteria or viruses, resulting in the intestines being unable to absorb fluid from the contents of the bowel
  • too much fluid is secreted into the bowel, causing "secretory diarrhoea" – this is often a sign of a bacterial infection
  • the contents of the bowel move through the digestive system too quickly, resulting in the intestines not having enough time to absorb fluid from them – this is often caused by anxiety or some types of medicine 
  • food, such as lactose, is not absorbed properly, causing water to move out of the blood and into the bowel, diluting the content

Diarrhoea usually occurs when fluid cannot be absorbed from the contents of your bowel, or when extra fluid is secreted into your bowel, causing watery faeces.

Short-term diarrhoea

Diarrhoea is usually a symptom of gastroenteritis (a bowel infection). It can be caused by:

Diarrhoea caused by contaminated food or water while visiting a foreign country is often known as travellers' diarrhoea.

Other possible causes of short-term diarrhoea include:


Diarrhoea can also sometimes be a side effect of medicines, including:

The patient information leaflet that comes with your medicine should state whether diarrhoea is a possible side effect.

You can also use the medicines A-Z to find out more about your medicine.

Long-term diarrhoea 

Conditions that can cause persistent diarrhoea include:

Persistent diarrhoea can also sometimes occur following a gastrectomy. This is a surgical operation to remove part of the stomach, for example as a treatment for stomach cancer.

Diarrhoea can also sometimes be caused by bariatric surgery (weight loss surgery used as a last resort to treat people who are dangerously obese).

Page last reviewed: 28/11/2012

Next review due: 28/11/2014


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