Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Diarrhea

What Is It?

Diarrhea is more frequent and more liquid bowel movements than normal. There are many causes. Diarrhea often is caused by an infection with bacteria, viruses or a parasite. Bacteria cause diarrhea either by invading the intestine or by producing a toxin that makes the intestine secrete more water. When the diarrhea is caused by food contaminated with bacteria or parasites, people often refer to this as food poisoning.

Other causes of diarrhea include:

• Irritable bowel syndrome, especially during times of increased stress

• Side effects from medications, such as antibiotics and magnesium-containing antacids

• Overuse of laxatives

• Inflammation of the lowest part of the intestine (ulcerative colitis or Crohn's disease).