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What is diarrhea?

Diarrhea is loose, watery stools. A person with diarrhea typically passes stool more than three times a day. People with diarrhea may pass more than a quart of stool a day. Acute diarrhea is a common problem that usually lasts 1 or 2 days and goes away on its own without special treatment. Prolonged diarrhea persisting for more than 2 days may be a sign of a more serious problem and poses the risk of dehydration. Chronic diarrhea may be a feature of a chronic disease.
Diarrhea can cause dehydration, which means the body lacks enough fluid to function properly. Dehydration is particularly dangerous in children and older people, and it must be treated promptly to avoid serious health problems. See Dehydration.
People of all ages can get diarrhea and the average adult has a bout of acute diarrhea about four times a year. In the United States, each child will have had seven to 15 episodes of diarrhea by age 5.

What causes diarrhea?

Acute diarrhea is usually related to a bacterial, viral, or parasitic infection. Chronic diarrhea is usually related to functional disorders such as irritable bowel syndrome or inflammatory bowel disease.

A few of the more common causes of diarrhea include the following:

Bacterial infections. Several types of bacteria consumed through contaminated food or water can cause diarrhea. Common culprits include Campylobacter, Salmonella, Shigella, and Escherichia coli (E. coli).

Viral infections. Many viruses cause diarrhea, including rotavirus, Norwalk virus, cytomegalovirus, herpes simplex virus, and viral hepatitis.

Food intolerances. Some people are unable to digest food components such as artificial sweeteners and lactose—the sugar found in milk.

Parasites. 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. Antibiotics, blood pressure medications, cancer drugs, and antacids containing magnesium can all cause diarrhea.

Intestinal diseases. Inflammatory bowel disease, colitis, Crohn’s disease, and celiac disease often lead to diarrhea.

Functional bowel disorders. Diarrhea can be a symptom of irritable bowel syndrome.

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 after gallbladder surgery.
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 parasites. Traveler’s diarrhea can be a problem for people visiting developing countries. Visitors to the United States, Canada, most European countries, Japan, Australia, and New Zealand do not face much risk for traveler’s diarrhea. See Preventing Traveler’s Diarrhea.
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.