What causes diarrhoea?

Viruses such as norovirus and rotavirus commonly irritate the gut and may cause sudden loose stools, vomiting, cramps, or fever. Giardiasis, traveller’s diarrhoea, and typhoid fever are other infectious possibilities, particularly after unsafe food or water or travel exposure.

Lactose intolerance can cause loose stools, wind, and cramps after dairy. Irritable bowel syndrome may produce diarrhoea alongside abdominal pain and altered bowel habits. Antibiotics, laxatives, magnesium-containing products, and some other medicines can change stool consistency. An overactive thyroid may speed up gut movement. The timing, duration, associated symptoms, diet, travel, and medicines help narrow the cause.

Drink regularly and replace fluids after each loose stool. Eat small, simple meals if hungry, and avoid foods that clearly worsen symptoms. Wash hands with soap and water, avoid preparing food for others while unwell, and review recent antibiotics, travel, restaurant meals, or new products.

Do not stop a prescribed medicine without advice. A clinician may recommend stool testing, blood tests, or a dietary review when symptoms persist, recur, or follow travel. Children, older adults, and people with other illnesses may become dehydrated more quickly.

Seek urgent help for blood or black stool, severe or worsening abdominal pain, confusion, fainting, persistent vomiting, signs of dehydration, or a high fever with marked weakness. Arrange medical review for diarrhoea that continues, repeatedly returns, follows recent antibiotics or travel, or affects a vulnerable person.

Could an infection, food intolerance, medicine, thyroid problem, or irritable bowel syndrome explain this pattern? Do I need testing? Which fluids and foods are suitable while symptoms continue?