Diarrhea is loose, watery, and frequent stool. Diarrhea is considered chronic (long-term) when you have had loose or frequent stools for more than 4 weeks.

Diarrhea in adults is usually mild and goes away quickly without complications. In infants and children (especially under age 3), diarrhea can cause dangerous dehydration fairly quickly.

The most common cause of diarrhea is viral gastroenteritis, a mild viral infection that goes away on its own within a few days. This condition is often called the stomach flu. Viral gastroenteritis often occurs in mini-epidemics in schools, neighborhoods, or families.

Food poisoning and traveler's diarrhea are two other common causes of diarrhea. They occur as a result of eating food or drinking water contaminated with bacteria or parasites.

Medications, especially antibiotics, laxatives containing magnesium, and chemotherapy for cancer treatment, can also cause diarrhea.

The following medical conditions can also lead to diarrhea:

• Celiac disease
• Inflammatory bowel diseases (Crohn's disease and ulcerative colitis)
• Irritable bowel syndrome (IBS)
• Malabsorption syndromes such as lactose intolerance

Other less common causes of diarrhea include:

• Carcinoid syndrome
• Nerve disorders like autonomic neuropathy or diabetic neuropathy
• Radiation therapy
• Partial removal of the stomach (gastrectomy)
• Zollinger-Ellison syndrome

• Drink plenty of fluid to avoid becoming dehydrated. Start with sips of any fluid other than caffeinated beverages. Milk may prolong loose stools, but also provides needed fluids and nourishment. Drinking milk may be fine for mild diarrhea. For moderate and severe diarrhea, electrolyte solutions available in drugstores are usually best.
• Active cultures of beneficial bacteria (probiotics) make diarrhea less severe and shorten its duration. Probiotics can be found in yogurt with active or live cultures and in supplements.
• Foods like rice, dry toast, and bananas can sometimes help with diarrhea.
• Avoid over-the-counter antidiarrhea medications unless specifically instructed to use one by your doctor. Certain infections can be made worse by these drugs. When you have diarrhea, your body is trying to get rid of whatever food, virus, or other bug is causing it. The medicine interferes with this process.
• Get plenty of rest.

If you have a chronic form of diarrhea, like the one caused by irritable bowel syndrome, try adding bulk to your diet -- to thicken the stool and regulate bowel movements. Such foods include fiber from whole-wheat grains and bran. Psyllium-containing products such as Metamucil or similar products can also add bulk to stools.

Call your doctor if:

• You have blood or pus in your stools or your stool is black
• You have abdominal pain that is not relieved by a bowel movement
• You have symptoms of dehydration such as light-headedness when sitting or standing up
• You have a fever above 101°F, or your child has a fever above 100.4°F, along with diarrhea
• You have foul-smelling or oily-looking stools
• You have recently traveled to a foreign country
• You have eaten with other people who also have diarrhea
• You have started on a new medication
• Your diarrhea does not get better in 5 days (2 days for an infant or child), or worsens before that
• Your child has been vomiting for more than 12 hours (in a newborn under 3 months you should call as soon as vomiting or diarrhea begins)

Your doctor will take a complete medical history and do a physical examination, paying careful attention to your abdomen.

Questions that the doctor may ask include:

• When did your diarrhea start?
• How long have you had diarrhea?
• What is the color and consistency of your stool?
• Do you have blood in your stool?
• Are you passing large amounts of mucus with your stool?
• What other symptoms do you have?
• Do you have abdominal pain or severe cramping with the diarrhea?
• Do you have fever or chills?
• Are any other family members sick?
• Have you recently traveled out of the country?
• What makes your pain worse? Stress? Specific foods?
• Have you had abdominal surgery?
• What medications do you take? Any recent changes to your medications?
• Do you drink coffee? How much?
• Do you drink alcohol? How much? How often?
• Do you smoke? How much each day?
• Are you on a special diet?

Your doctor will ask you to obtain one or more stool samples in special containers to test for signs of inflammation and infection and to identify the organism causing infection.

If there are signs of dehydration in addition to the diarrhea, your doctor may order:

• Basic metabolic panel (to check electrolyte levels)
• BUN and creatinine tests
• Urine specific gravity

• Wash your hands often, especially after going to the bathroom and before eating.
• Teach children to not put objects in their mouth.
• When taking antibiotics, try eating food with Lactobacillus acidophilus, a healthy bacteria. This helps replenish the good bacteria that antibiotics can kill. Yogurt with active or live cultures is a good source of this healthy bacteria.
• Use alcohol-based hand gel frequently.

When traveling to underdeveloped areas, follow the steps below to avoid diarrhea:

• Drink only bottled water and do NOT use ice.
• Do NOT eat uncooked vegetables or fruits that do not have peels.
• Do NOT eat raw shellfish or undercooked meat.
• Do NOT consume dairy products.

Semrad CE, Powell DW. Approach to the patient with diarrhea and malabsorption. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders; 2007:chap 143.

Proctor DD. Approach to the patient with gastrointestinal disease. In: Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders; 2007:chap 134.