Causes of diarrhea include - bacteria from contaminated food or water - viruses that cause illnesses such as the flu - parasites, which are tiny organisms found in contaminated food or water - medicines such as antibiotics - problems digesting certain foods - diseases that affect the stomach, small intestine, or colon, such as Crohns disease - problems with how the colon functions, caused by disorders such as irritable bowel syndrome Sometimes no cause can be found. As long as diarrhea goes away within 1 to 2 days, finding the cause is not usually necessary. 
What causes What I need to know about Diarrhea ?