Parasites can enter the body through food or water and settle in the digestive system. Parasites that cause diarrhea include Giardia lamblia, Entamoeba histolytica, and Cryptosporidium. Reaction to medicines, such as antibiotics, blood pressure medications, and antacids containing magnesium. Intestinal diseases, like inflammatory bowel disease or celiac disease. Functional bowel disorders, such as irritable bowel syndrome, in which the intestines do not work normally.
Some people develop diarrhea after stomach surgery or removal of the gallbladder.
The reason may be a change in how quickly food moves through the digestive system after stomach surgery or an increase in bile in the colon that can occur after gallbladder surgery. In many cases, the cause of diarrhea cannot be found. As long as diarrhea goes away on its own, an extensive search for the cause is not usually necessary. People who visit foreign countries are at risk for traveler's diarrhea, which is caused by eating food or drinking water contaminated with bacteria, viruses, or, sometimes, parasites. Traveler's diarrhea is a particular problem for people visiting developing countries.