Diarrhoea - Causes 

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:

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

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:

• emotional upset or anxiety
• drinking too much coffee or alcohol
• a food allergy
• appendicitis (painful swelling of the appendix)
• damage to the lining of the intestines due to radiotherapy 

Medicines

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

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

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:

• bowel cancer - which can cause diarrhoea and blood in your stools
• chronic pancreatitis - inflammation of the pancreas, a small organ that produces hormones and digestive juices
• coeliac disease - a digestive condition where you are intolerant to the protein gluten
• Crohn's disease - a condition that causes inflammation of the digestive system lining 
• irritable bowel syndrome (IBS) - a poorly understood condition where the normal functions of the bowel are disrupted 
• microscopic colitis - a type of inflammatory bowel disease that causes watery diarrhoea 
• ulcerative colitis - a condition that affects the colon (large intestine)
• cystic fibrosis - an inherited condition that affects the lungs and digestive system 

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 that is used as a last resort to treat people who are dangerously obese).