Bright green diarrhoea: what it can mean and what to do

Bile starts green and normally becomes brown as it travels through the intestine. When diarrhoea passes quickly, there may be less time for that colour change. Green foods, colouring, leafy vegetables and some supplements can have a similar effect. Sudden loose stools with cramps, nausea or fever may occur with gastroenteritis or food poisoning. Ongoing symptoms, weight loss, bloating or greasy stools need a clinical assessment because food intolerance, coeliac disease, inflammatory bowel disease, giardiasis or an overactive thyroid can also affect bowel habits.

Drink frequent small amounts of water, oral rehydration solution or clear fluids. Continue light meals if you feel able, choosing foods that are easy to tolerate, and avoid alcohol. Wash your hands carefully and avoid preparing food for other people while diarrhoea continues. Note when it began, how often you pass stool, what you ate, any new medicine and whether blood, mucus, fever or vomiting is present. Do not take an anti-diarrhoeal medicine if you have blood in the stool or a high fever without medical advice.

Arrange medical advice if diarrhoea persists, keeps returning, or follows recent travel, antibiotics or a change in treatment. Seek urgent help for severe or worsening abdominal pain, faintness, confusion, very little urine, a dry mouth with inability to drink, black or bloody stool, repeated vomiting or a high fever. Babies, older adults, pregnant people and anyone with a long-term illness can become dehydrated more quickly and should seek advice sooner.

Could a recent meal, medicine or supplement explain the colour? Do I need testing for infection or inflammation? Which fluids and foods are suitable for me? What symptoms should prompt urgent review?