Causes of diarrhea

Sudden diarrhea commonly follows gastroenteritis or food poisoning, when infection or toxins irritate the gut. Giardiasis is another infectious cause, especially after exposure to unsafe water. Antibiotics and some other medicines can alter the bowel. Certain foods may trigger symptoms through food intolerance.

Recurring or persistent diarrhea can occur with irritable bowel syndrome, coeliac disease, Crohn's disease, or an overactive thyroid. The pattern matters: note duration, stool appearance, pain, fever, travel, new medicines, and any link with meals. A cause cannot be confirmed from stool frequency alone.

Drink frequent small amounts of water or oral rehydration fluid, and eat simple foods as tolerated. Wash hands carefully and avoid preparing food for others while an infection is possible. Do not start antibiotics or restrictive diets without advice. Arrange medical review if diarrhea keeps returning, follows travel, begins after a medicine, or is affecting hydration, work, or sleep.

Seek urgent care for blood or black stool, severe or worsening abdominal pain, fainting, confusion, very little urine, inability to keep fluids down, or signs of serious dehydration. Fever with marked weakness, or diarrhea in a person who is medically vulnerable, also warrants prompt advice.

Ask whether infection, food intolerance, medicine effects, or an ongoing condition is more likely, whether tests are needed, and how to replace fluids safely.