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Understanding Diarrhea -- the Basics

What Is Diarrhea?

Doctors usually define diarrhea as a significant increase in the total weight of stool passed in a single day. 

Most people, however, think of diarrhea as an illness during which they have more frequent, loose, watery stools.

Understanding Diarrhea

Almost everyone has diarrhea at some point in his or her life. In developing countries, where illnesses that cause diarrhea are more common and where health care is less readily available, diarrhea is a major health concern because of its potential to cause severe, life-threatening dehydration. Infants and the elderly are more prone to dehydration from diarrhea.


Diarrhea that comes on suddenly and goes away over a period of a couple of weeks is usually referred to as "acute diarrhea." Most people with acute diarrhea recover on their own. 

Diarrhea that lasts more than four weeks is thought of as "chronic diarrhea." Typically, chronic diarrhea requires medical care to find the underlying cause and treat complications, such as dehydration.

What Causes Diarrhea?

Many different things can cause diarrhea. Here are the major causes.


You are most likely to come down with diarrhea after coming into contact with these infectious organisms and agents:

  • A virus, such as rotavirus, Norwalk agent, enterovirus, or a hepatitis virus
  • A bacterium, such as E. coli, salmonella, shigella, clostridium, or Vibrio cholerae
  • A parasite, such as those that cause giardiasis and amebiasis

You may pick up an infectious agent from contact with another individual who has it, or you may get it after eating contaminated food or drinking contaminated water. If you eat food that was improperly cooked or was contaminated after cooking, you may get food poisoning, which can lead to diarrhea. Children who attend day care and their families are more likely to be exposed to certain infectious agents.

Many people who travel to foreign countries develop what is termed "traveler's diarrhea," usually after drinking contaminated water. Infectious diarrhea is a particular hazard in developing countries, where it may be difficult to keep waste water and sewage separate from water used for cooking, drinking, and bathing and where inadequate facilities make it difficult to practice good personal hygiene.

Other Medical Conditions

A number of noninfectious medical conditions may cause diarrhea. These include:

  • Inability to digest certain foods, including lactose intolerance (difficulty digesting sugar found in dairy products); celiac disease (an immune reaction to consuming gluten, a protein found in wheat, barley, and rye); and pancreatic problems, such as those caused by cystic fibrosis, which interfere with production of important digestive substances.
  • Surgery to remove part of your small intestine. A shortened small intestine may be unable to absorb all the substances you eat. This is referred to as short-bowel syndrome.
  • Surgical removal of the gallbladder. An increase in bile in the colon may result in watery stools.
  • Certain diseases of the endocrine (hormonal) system, including overactive thyroid disease, diabetes, adrenal disease, and Zollinger-Ellison syndrome
  • Certain rare tumors (including carcinoid tumor and pheochromocytoma) that produce diarrhea-causing substances (hormones)
  • Inflammation in the intestinal tract, which can result in chronic diarrhea. If you have inflammatory bowel disease (such as ulcerative colitis, Crohn's disease, or microscopic colitis), you will have regular bouts of diarrhea during a flare-up of your disease.
  • Irritable bowel syndrome, which may cause alternating bouts of diarrhea and constipation
  • Ischemic bowel disease, which can be caused by blocked arteries. Symptoms might include abdominal pain with bloody diarrhea.


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