Prolonged diarrhea, Chronic diarrhea of unknown origin, Chronic small bowel diarrhea, Chronic large bowel diarrhea. Root Cause of Disease A wide range of problems can cause chronic diarrhea; some of the most common causes include irritable bowel syndrome (IBS), inflammatory bowel disease (Crohn disease and ulcerative colitis), malabsorption syndromes, like celiac disease, in which food…