Sudden diarrhoea, with or without vomiting, is usually caused by an infection of the gut (gastroenteritis). It may come from contaminated food or water, or spread from person to person. Most people recover within one to three days.
Common causes
- Viruses, such as norovirus, which spread easily in families and offices and cause sudden vomiting
- Bacteria, such as Salmonella and Campylobacter, from undercooked chicken, eggs or contaminated food
- Toxins already in the food, for example from cooked rice or dishes left out at room temperature. These cause vomiting within a few hours of eating.
What to do
- Drink enough: take small, frequent sips. Oral rehydration salts from a pharmacy are best, as they replace salt and sugar as well as water.
- Eat when you feel ready: start with plain food such as porridge, rice, bread, crackers or bananas
- Rest, and wash your hands well to protect others
- Most people do not need antibiotics, as they do not help viral infections and most bacterial ones settle on their own
- Avoid anti-diarrhoea medicine if there is blood in the stool or a fever
See a doctor if
- You cannot keep fluids down, or have signs of dehydration: dizziness, a dry mouth, or passing very little urine
- There is blood in the stool, a high fever, or severe abdominal pain
- It lasts more than three days, or started after travel
- You are elderly, pregnant, or have a weakened immune system, kidney disease or diabetes
Diarrhoea that lasts four weeks or more is not food poisoning; see chronic diarrhoea. Some people have ongoing bowel symptoms after a gut infection, a form of IBS, which usually improves over time.
Seek urgent care at an emergency department for confusion, fainting, very little or no urine, heavy bleeding, or severe abdominal pain.
General information only. Reviewed by Dr Chia Chung King, 2026-11-13. Book a consultation.