In medicine, diarrhea (from the Greek, "diarrhoia" meaning "a flowing through"[1]), also spelled diarrhoea (see spelling differences), is characterized by frequent loose or liquid bowel movements. Acute diarrhea is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause severe dehydration which is one cause of death in diarrhea sufferers. Along with water, sufferers also lose dangerous amounts of important salts, electrolytes, and other nutrients.

Causes
See also: List of causes of diarrhea
 
Diagram of the human gastrointestinal tract.Diarrhea commonly results from gastroenteritis caused by viral infections, parasites or bacterial toxins.[2] In sanitary living conditions where there is ample food and a supply of clean water, an otherwise healthy patient usually recovers from viral infections in a few days. However, for ill or malnourished individuals diarrhea can lead to severe dehydration and can become life-threatening without treatment.[3]

Diarrhea can also be a symptom of more serious diseases, such as dysentery, cholera, or botulism, and can also be indicative of a chronic syndrome such as Crohn's disease or severe mushroom poisoning syndromes. Though appendicitis patients do not generally have violent diarrhea, it is a common symptom of a ruptured appendix. It is also an effect of severe radiation sickness.

Diarrhea can also be caused by dairy intake in those who are lactose intolerant.

Symptomatic treatment for diarrhea involves the patient consuming adequate amounts of water to replace that loss, preferably mixed with electrolytes to provide essential salts and some amount of nutrients. For many people, further treatment is unnecessary. The following types of diarrhea indicate medical supervision is required:

Diarrhea in infants
Moderate or severe diarrhea in young children;
Diarrhea associated with blood
Diarrhea that continues for more than two days;
Diarrhea that is associated with more general illness such as non-cramping abdominal pain, fever, weight loss, etc;
Diarrhea in travelers, since they are more likely to have exotic infections such as parasites;
Diarrhea in food handlers, because of the potential to infect others;
Diarrhea in institutions such as hospitals, child care centers, or geriatric and convalescent homes.
A severity score is used to aid diagnosis in children.