What should you know about extreme diarrhoea?

Loose or watery stools can follow an infection such as gastroenteritis, food poisoning, or giardiasis. Food intolerance, coeliac disease, irritable bowel syndrome, Crohn's disease, or an overactive thyroid can also cause diarrhoea, particularly when symptoms recur or continue beyond a short illness.

The main immediate concern is loss of water and electrolytes. Warning signs include a very dry mouth, dark or reduced urine, marked weakness, dizziness, drowsiness, or difficulty keeping fluids down.

Take frequent small sips of water and an oral rehydration solution if available. Eat light foods as tolerated, such as rice, toast, bananas, or soup, and avoid alcohol and foods that clearly worsen symptoms. Wash hands carefully and avoid preparing food for others while infectious diarrhoea is possible. Do not use anti-diarrhoeal medicine if you have blood in the stool or a high fever unless a clinician advises it.

Get urgent medical help for blood or black stool, severe or worsening abdominal pain, fainting, confusion, repeated vomiting, signs of dehydration, or inability to drink. Seek prompt assessment for diarrhoea after recent antibiotics, during pregnancy, in a young child or older adult, or when it does not begin to settle.

Tell the clinician when symptoms began, how often stools occur, their appearance, recent travel, unsafe food or water, antibiotics, sick contacts, fever, pain, and weight change. Ask whether stool tests, blood tests, or a review for food triggers is appropriate.