Diarrhoea - Causes of diarrhoea

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 poo.

Short-term diarrhoea

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

a virus – such as norovirus or rotavirus
bacteria – such as campylobacter, Clostridium difficile (C. difficile), Escherichia coli (E. coli), salmonella or shigella; these can all cause food poisoning
parasites – such as the Giardia intestinalis parasite that causes giardiasis

Other possible causes of short-term diarrhoea include:

feelings of anxiety
drinking too much alcohol
a food allergy
appendicitis
damage to the lining of the intestines as a result of radiotherapy

Medicines

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

antibiotics
antacid medicines that contain magnesium
some chemotherapy medicines
non-steroidal anti-inflammatory drugs (NSAIDs)
selective serotonin reuptake inhibitors (SSRIs)
statins (cholesterol-lowering medicines)
laxatives (medicine used to help empty your bowels)

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 about your medicine.

Long-term diarrhoea

Conditions that can cause persistent diarrhoea include:

irritable bowel syndrome (IBS) – a poorly understood condition affecting the normal functions of the bowel
inflammatory bowel disease – conditions that cause the gut to become inflamed, such as Crohn's disease and ulcerative colitis
coeliac disease – a digestive condition where you have an adverse reaction to gluten
chronic pancreatitis – inflammation of the pancreas
diverticular disease – where small bulges or pockets develop in the lining of the intestine
bowel cancer – this can cause diarrhoea and blood in your stools

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