What causes diarrhea?

Too much fluid is passed (secreted) from the blood-stream into the bowel, for example in gastroenteritis. This is how some laxatives work.
The bowel moves its contents through too quickly and too little fluid is passed back into the bloodstream. This is one way in which anxiety produces diarrhea.
More liquid is drunk than the bowel can cope with – this seldom happens, but is one way in which drinking too much beer can cause diarrhea.

What causes acute diarrhea?

Food poisoning
Gastroenteritis (see separate leaflet on the prevention and treatment of travellers’ diarrhea)
Anxiety
Sometimes treatment with an antibiotic
Alcohol (to excess)

What causes chronic diarrhea?

When diarrhea goes on for a long time, the most likely cause is irritable bowel syndrome. It is called a ‘functional’ condition. This means that the bowel produces stools which are looser or more frequent than normal, although the bowel is not diseased.