Diarrhea: Causes, Symptoms & Treatments

stomach cramps
Stomach cramps are one of the symptoms of diarrhea.
Credit: Piotr Marcinski | shutterstock

Diarrhea — or loose, watery bowel movements that occur more frequently than usual — is one of the most commonly reported ailments in the United States (second only to respiratory infection), according to the American College of Gastroenterology (ACG). While diarrhea does not typically cause serious complications for most patients, it can be a fatal ailment for young children, especially those who are malnourished or have compromised immune systems, according to the World Health Organization (WHO).

Types of diarrhea and causes

A bout of diarrhea that lasts no more than two weeks is referred to as acute diarrhea and is most often caused by a viral infection, according to the ACG. The most common diarrhea-causing virus for adults is norovirus, which is often referred to as "cruise ship diarrhea" due to its unfortunate tendency to infect sea-faring vacationers. Rotavirus, another diarrhea-inducing virus, is very common in young children.

Other causes of acute diarrhea include bacterial infection, which is often referred to as "traveler's diarrhea," or, in some parts of the world, "Montezuma's revenge." But those who come down with this uncomfortable ailment aren't the victims of an ancient curse; they're usually the victims of the bacteria enterotoxigenic Escherichia coli (ETEC), according to Dr. Ian Lustbader, a clinical associate professor of medicine and a gastroenterologist at New York University's Langone Medical Center.

A final common cause of acute diarrhea is parasites, which can be ingested when a person consumes contaminated food or water, Lustbader told Live Science. 

Diarrhea that lasts longer than four weeks is known as chronic diarrhea. Like acute diarrhea, chronic diarrhea has many causes. According to Lustbader, these causes include: 

  • Infectious causes (most commonly parasites)
  • Osmotic and malabsorption causes (which result in too much water being absorbed into the bowel), such as Celiac disease and lactose intolerance
  • Inflammatory causes, such as ulcerative colitis or Crohn's disease
  • Intestinal ischemia, or lessened blood flow to the intestine 
  • Certain cancer therapies, like radiation
  • Certain medications, such as antibiotics


"Diarrhea can be nothing to worry about, or it can be potentially life-threatening," said Lustbader, who explained that the underlying cause of a patient's diarrhea is what determines the seriousness of this uncomfortable ailment.  

The primary complication of diarrhea is dehydration caused by the loss of large amounts of water, salt and nutrients. According to the Mayo Clinic, dehydration can lead to other serious conditions such as low blood pressure, seizures, kidney failure or even death. Those with ongoing diarrhea should seek medical attention if they experience:

  • Dark urine or small amounts of urine
  • Rapid heart rate
  • Dry, flushed skin
  • Headaches or light-headedness
  • Fatigue
  • Irritability or confusion
  • Severe abdominal or rectal pain
  • Blood in the stool or black, tar-like stools

Diagnosis & tests

Diagnosing diarrhea itself isn't always as simple as one might think, said Lustbader, who noted that people often experience changes in their bowel movements and think that they have diarrhea when, in fact, they do not. But if a patient is having three or more watery or soft bowel movements a day, then they likely do have diarrhea, Lustbader said. 

To diagnose diarrhea, a doctor may want to determine the condition’s cause, especially for patients whose symptoms are severe and/or ongoing. According to the National Institutes of Health (NIH), diagnostic tests for diarrhea include:

  • Physical exam of the abdomen and questions about eating habits
  • Medication review, including over-the-counter drugs and supplements
  • Blood tests to rule out certain diseases
  • Stool culture to determine whether bacteria or parasites are present
  • Fasting tests, avoiding various foods to determine whether diarrhea responds to dietary changes
  • Sigmoidoscopy or colonoscopy, which allow doctors to view the colon and rectum internally
  • Imaging tests to rule out intestinal blockages or other abnormalities

Treatment & medication

Most cases of diarrhea resolve spontaneously within a few days and all that is needed is preventing dehydration by replacing lost fluids, according to the NIH.

In the meantime, various over-the-counter medications may help firm the stool and decrease the urgency for bowel movements. These include loperamide hydrochloride (commonly known as the brand name Imodium AD), bismuth subsalicylate (Pepto-Bismol) and attapulgite (Kaopectate). 

These medications, however, are not recommended for diarrhea caused by bacterial infection or parasites, according to the NIH, because organisms will be trapped in the intestines if the diarrhea ceases before they are completely excreted.

The Cleveland Clinic recommends drinking two to three quarts or liters of liquids daily while recovering from diarrhea. While water is fine, it does not replace lost salt or nutrients, so better choices are broth, tea with honey, sports drinks and pulp-free juices. Avoid milk products, caffeine, alcohol, and apple and pear juices, because they may worsen diarrhea.

Soft, bland foods are recommended as well, including bananas, plain rice, toast, crackers, boiled potatoes, smooth peanut butter, cottage cheese, noodles and applesauce. Because yogurt, cheese and miso contain probiotics, which contain strains of bacteria similar to those in a healthy intestine, they are also good choices. Avoid fatty, high-fiber or heavily seasoned foods for several days. 

Lustbader also recommends taking steps to prevent diarrhea, especially when traveling. These measures include drinking only bottled or boiled water, frequently washing your hands (especially before eating) and eating only freshly cooked foods.

Follow Elizabeth Palermo @techEpalermo. Follow Live Science @livescience, Facebook & Google+.

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Elizabeth Palermo

Elizabeth Palermo

Elizabeth is a Live Science staff writer who writes about science and technology. She graduated with a B.A. from the George Washington University. Elizabeth has traveled throughout the Americas, studying political systems and indigenous cultures and teaching English to students of all ages.
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