When you have diarrhea, your bowel movements (or stools) are loose and watery. It’s very common and usually not serious.
Many people get diarrhea once or twice each year. It normally lasts 2 to 3 days, and you can treat it with over-the-counter medicines. Some people get it more often as part of irritable bowel syndrome (IBS) or other conditions.
Usually, diarrhea is caused by a virus that infects your gut. Some people call it "intestinal flu" or "stomach flu."
Other causes include:
Allergies to certain foods
Diseases of the intestines (such as Crohn's disease or ulcerative colitis)
Eating foods that upset the digestive system
Infection by bacteria (the cause of most types of food poisoning) or other organisms
Overactive thyroid (hyperthyroidism)
Running (Some people get “runner’s diarrhea” for reasons that aren’t clear)
Surgery on your digestive system
Trouble absorbing certain nutrients, also called “malabsorption”
Diarrhea may also follow constipation, especially for people who have irritable bowel syndrome.