Normal stool frequency ranges from three times per week to three times per day. Diarrhoea may be defined as an excess of stool being passed, usually accompanied by an increased frequency and liquidity of the stool.

Diarrhoea may be accompanied by abdominal and rectal pain, urgency to go, and incontinence. If the diarrhoea is caused by food poisoning, there may be concomitant vomiting. The diarrhoeal stool is more liquid than usual, may contain more fats when caused by malabsorption (steatorrhoea) and may contain pus or blood in cases of bowel inflammation. Diarrhoea is usually acute or of short duration, although it can be chronic or long lasting.

More Information about Diarrhoea

Osmotic diarrhoea

Lactase deficiency can be hereditary or acquired. Lactase is the enzyme that splits lactose, the milk sugar, into the absorbable monosaccharides glucose and galactose. Without lactase, lactose remains in the intestine, creating an osmotic load, meaning that more water remains in the intestine leading to watery stools. Other causes of this type of ‘osmotic load’ diarrhoea include artificial sweeteners such as sorbitol, and laxatives such as lactulose or magnesium sulphate. Malabsorption can cause steatorrhoea, which is increased fat content in the stools; this is usually identified by large pale floating stools with an unpleasant odour.


Increased motility of the gut can increase the frequency of defecation, and in severe cases there may be a barrier to reabsorption of fluids from the stool, resulting in increased stool volume. This may occur with autonomic neuropathy in cases of diabetes mellitus. Most acute diarrhoea is acute and self-limiting due to bacterial or viral infection, and the diarrhoea is a defence mechanism to rid the body of the offending organism. In these cases, anti-diarrhoeal drugs should not be used. Treatment should be the administration of fluids and electrolytes.