This is a somewhat difficult question to answer, because everyone has diarrhea on occasion, which is normal. Pathologic diarrhea has several definitions – several loose stools per day, stools greater than a cup in size, stools that occur throughout the night, and loose stools that persist for several weeks. Most cases of diarrhea simply resolve, so determining the appropriate time to pursue the cause of diarrhea is another issue.


Again, most cases resolve despite efforts by you or your doctor. On occasion diarrhea is severe and requires prompt attention from a physician. Any diarrheal illness that lasts over a month should be evaluated. Bloody diarrhea is cause for concern. Fevers, chills, abdominal pain, dizziness, or change in consciousness accompanying diarrhea signifies potentially serious illness and should be promptly evaluated.


The list of diarrheal etiologies is endless. Some of the more common causes will be reviewed below.

Infections – We have hundreds of bacteria that normally live in our intestines and perform an important function. Once in a while, one of these can become overgrown and wreak havoc. Bacteria such as E coli 0157:H7, Salmonella, Shigella and Campylobacter are typically ingested from contaminated food or water sources. Parasites like Giardia or amoeba come from similar sources. Clostridium difficile is associated with antibiotic use. A whole host of viruses can cause diarrhea. Patients whose immune systems function improperly, as in AIDS or chronic steroid use, are at particular risk for intestinal infections.

Medications – It is not unusual to develop diarrhea when new medication is started. Sometimes the diarrhea will resolve, and sometimes it is necessary to stop the medication.

Inflammatory conditions – Inflammation can occur at any spot along the entire GI tract. When enough inflammation accumulates, diarrhea can result from improper management of water and nutrients. A number of inflammatory conditions exist including Crohn’s disease, ulcerative colitis, ischemic colitis, microscopic colitis and various other ulcerating diseases.

Irritable bowel syndrome – Also called spastic colon or functional bowel disorder, IBS is poorly understood in terms of cause and treatment. We believe the bowels squeeze in an uncoordinated manner and manage fluid within the GI tract improperly, which can at times cause diarrhea, and other times constipation. Other symptoms include abdominal pain and bloating. This condition may be aggravated by increased stress.

Food and other oral substances – This category can be daunting, as practically anything we put in our mouths at one point or another can cause diarrhea. Sometimes there are patterns, however. Certain foods such as dairy products, spicy foods or greasy food may cause diarrhea. Celiac sprue is a disease where the small bowel is allergic to gluten, a common ingredient in many grains. Patients can have diarrhea, weight loss, skin rashes and lactose intolerance. Artificial sweeteners, particularly sorbitol, will cause excessive diarrhea in some patients. Laxatives can be mistakenly or intentionally ingested, and their purpose is to induce loose stools. Milk of Magnesia, Ex-Lax, Senna, and Dulcolax are some of the more popular brands. Any over-the-counter preparation containing magnesium can cause diarrhea, such as Maalox or Mylanta.

Cancer or growths – On rare occasions, partial obstruction of the colon from cancer will result in diarrhea. Other benign and malignant growths in the bowel can also produce diarrhea by stimulating flow of excessive water into your colon.


Your physician can learn a great deal from the history of your diarrheal illness. He or she may choose to collect stool for studies, perform radiographic imaging like CT scan, or do colonoscopy. Therapy depends on how ill you are in general, and whether a cause of diarrhea can be found. In some cases it is safe to use over-the-counter or prescription anti-diarrheal agents like Imodium, Pepto-Bismol, Kaopectate or lomotil.