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Diarrhea is described as an increase in the frequency of bowel movements or a decrease in the consistency of stools that causes the discharge of watery, loose stools. The severity of diarrhea is determined by the size and number of stools passed within a period of time.

• Severe diarrhea means having more than 10 loose, watery stools in a single day (24 hours).
• Moderate diarrhea means having more than a few but not more than 10 diarrhea stools in a day.
• Mild diarrhea means having a few diarrhea stools in a day.

Severe diarrhea has many causes. Stomach flu (gastroenteritis) or food poisoning may cause severe diarrhea. Drinking untreated water that contains the Giardia lamblia parasite can cause diarrhea that develops 1 to 4 weeks later.

Severe diarrhea increases your risk of dehydration by causing your body to lose large amounts of fluid quickly. Be sure to increase your intake of fluids, such as water or a rehydration drink, and to watch for symptoms of dehydration.

Persistent diarrhea can have many causes, including dietary changes, stress, irritable bowel syndrome, and certain medicines. Occasionally, persistent diarrhea can be a symptom of a more serious condition, such as a chronic infection, inflammatory bowel disease, a malabsorption syndrome, or colorectal cancer.