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Diarrhea

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Medical Author: Jay W. Marks, MD
Medical Editors: Dennis Lee, MD and William C. Shiel, Jr., MD, FACP, FACR

Diarrhea Causes

Common Causes of Chronic Diarrhea

Examples of some of the common causes of chronic diarrhea include:

infectious disease such as Giardia lamblia;
following acute viral, bacterial, or parasitic infections;
severe constipation;
laxative abuse; and
endocrine diseases such as hyperthyroidism or Addison's disease.

Diarrhea also can be a symptom of a disease or condition. For example:

fat malabsorption can cause diarrhea as a symptom of celiac disease,
irritable bowel syndrome (IBS),
bacterial overgrowth of the small intestine (a condition in which normal colonic bacteria spread from the colon into the small intestine), and
inflammatory bowel disease (IBD) such as Crohn's disease and ulcerative colitis.

Read about more causes of chronic diarrhea »

What is diarrhea?

Diarrhea is an increase in the frequency of bowel movements or a decrease in the form of stool (greater looseness of stool). Although changes in frequency of bowel movements and looseness of stools can vary independently of each other, changes often occur in both.

Diarrhea needs to be distinguished from four other conditions. Although these conditions may accompany diarrhea, they often have different causes and different treatments than diarrhea. These other conditions are:

incontinence of stool, which is the inability to control (delay) bowel movements until an appropriate time, for example, until one can get to the toilet

rectal urgency, which is a sudden urge to have a bowel movement that is so strong that if a toilet is not immediately available there will be incontinence

incomplete evacuation, which is a sensation that another bowel movement is necessary soon after a bowel movement, yet there is difficulty passing further stool the second time

bowel movements immediately after eating a meal

How is diarrhea defined?

Diarrhea can be defined in absolute or relative terms based on either the frequency of bowel movements or the consistency (looseness) of stools.

Frequency of bowel movements. Absolute diarrhea is having more bowel movements than normal. Thus, since among healthy individuals the maximum number of daily bowel movements is approximately three, diarrhea can be defined as any number of stools greater than three. Relative diarrhea is having more bowel movements than usual. Thus, if an individual who usually has one bowel movement each day begins to have two bowel movements each day, then diarrhea is present-even though there are not more than three bowel movements a day, that is, there is not absolute diarrhea.

Consistency of stools. Absolute diarrhea is more difficult to define on the basis of the consistency of stool because the consistency of stool can vary considerably in healthy individuals depending on their diets. Thus, individuals who eat large amounts of vegetables will have looser stools than individuals who eat few vegetables. Stools that are liquid or watery are always abnormal and considered diarrheal. Relative diarrhea is easier to define based on the consistency of stool. Thus, an individual who develops looser stools than usual has diarrhea--even though the stools may be within the range of normal with respect to consistency.