Diarrhea that lasts only one to two days can be caused by an infection from bacteria, a virus, or a parasite. It may occur because of a flu bug you have contracted or because you ate contaminated food or water.

Food intolerances, such as lactose intolerance, and reactions to medications can also cause diarrhea. Long-lasting cases of diarrhea can be due to conditions that affect intestinal health, such as irritable bowel syndrome.

Diarrhea occurs when food passes too quickly through your colon. Normally your colon absorbs liquid from the food you eat, resulting in semi-hard stool; if food passes through too quickly, this absorption does not have time to occur and the results are loose or watery bowel movements.