Diarrhea is a medical term used to describe an increase in the liquidity or volume of stool or the frequency of bowel movements. Diarrhea is usually described as loose, watery stools, and patients with diarrhea may also experience abdominal pain, abdominal cramping, fever, nausea or blood in the stool.

Different processes in the body may promote diarrhea. These include a failure of the intestines to absorb adequate nutrients and fluids during digestion, the release of too much fluid into the digestive tract or complications that result from intestinal disorders.

Diarrhea can be short-term (acute) or long-term (chronic) in duration. Both types can range in severity, but acute diarrhea lasts for less than four weeks whereas chronic diarrhea continues for more than four weeks.

The most common cause of acute diarrhea is a viral infection (e.g., stomach flu) or bacteria or parasites consumed through contaminated food or water (e.g., food poisoning, traveler's diarrhea).

Chronic diarrhea may indicate a more serious problem, such as irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD). In addition, diarrhea can be a side effect of many different medications, especially antibiotics. Caffeine, alcohol, artificial sweeteners and dairy products may also cause diarrhea in some people. In these cases, the diarrhea usually stops when use of the aggravating agent is discontinued.

Because diarrhea is a symptom of other problems, treatment options will depend on the cause of the diarrhea. In patients with a viral infection, the diarrhea is usually left untreated and resolves itself within a few days. When the diarrhea is caused by certain foodborne bacteria or parasites (e.g., certain forms of E. coli and salmonella), antibiotics may be required to treat the infection. For chronic conditions, such as IBS or IBD, specific medical treatment may be required.

The symptoms of diarrhea, whether acute or chronic, can sometimes be relieved with various over-the-counter and prescription medications. Patients should check with their physician before use, since some of these may interfere with other medications or prolong any infection that might be causing the diarrhea. If a patient is dehydrated as a result of diarrhea, lost fluids and electrolytes will need to be replaced. For most people, this means drinking more fluids until the diarrhea resolves. However, intravenous hydration may be necessary for certain populations for whom diarrhea can become life-threatening such as the very young, the elderly and people with compromised immune systems. 

Diarrhea is an increase in the liquidity and/or volume of stool or the frequency of bowel movements. It may be mild, moderate or severe and can have an impact on normal activities. The average frequency of bowel movements and firmness of stool can vary greatly from person to person. Thus, it is important to note any significant changes in what is normal for a particular person. In patients with diarrhea, stool can range from soft to liquid in texture, brown to clear in color, and defecation may occur more than three times a day.

Diarrhea is caused by a disruption of the normal process of digestion. Normal digestion involves food traveling from the stomach to the small intestine, where most nutrients are absorbed. By the time it gets to the colon, only waste material remains. The colon absorbs most of the water from the waste and passes the stool along via muscle contractions (peristalsis) to the rectum at the end of the digestive tract. Diarrhea occurs when too much fluid remains in the intestines as stool travels through the digestive tract. When this occurs, the stool that is eventually passed through the anus is loose and watery.

Too much fluid in the intestines can be caused by several different types of digestive dysfunction, including:

• The small intestine and colon may fail to absorb enough nutrients and fluids from stool, making the stool loose and watery.
  
  
• The intestines may be stimulated to secrete water, salt or other fluids into the digestive tract, making stool runny. This stimulation can occur as the result of infection, disease or the presence of certain other substances (e.g., castor oil, excess bile acids).
  
  
• Food may pass through the intestines too quickly or in too large an amount to be properly absorbed. The rapid transit of stool through the digestive tract is a common cause of diarrhea.

Diarrhea is a common experience. Millions of Americans report problems with diarrhea every year. It is estimated that the average adult experiences diarrhea approximately four times a year, according to the National Institutes of Health (NIH). It may be difficult to identify exactly how many people have diarrhea, since most people do not seek medical treatment.

Acute diarrhea (lasting less than four weeks) is the most common type of diarrhea. According to the American College of Gastroenterology, it is the second most common reported illness in the United States, after respiratory infections. Most cases of acute diarrhea are caused by infections or antibiotics. Most episodes of acute diarrhea resolve spontaneously (without medications or with simple dietary changes).

Diarrhea is a common symptom of many different problems. It often appears with other symptoms, which may help physicians determine their underlying cause. For example, patients with diarrhea due to infection may also experience abdominal pain, abdominal cramping, fever and blood in the stool, especially when the diarrhea is caused by infection. Nausea and vomiting may also occur with gastrointestinal infections.

Specific combinations of symptoms and their likely causes include:

• Chronic diarrhea. This may be a symptom of lactose or sorbitol intolerance, infection or irritable bowel syndrome (IBS). Additional symptoms of abdominal bloating and excessive gas after consuming dairy products may indicate lactose intolerance. When diarrhea is accompanied by alternating episodes of constipation, as well as abdominal pain and frequent bowel movements, it may indicate IBS. However, patients with these symptoms should seek professional medical advice and not assume these symptoms are due to IBS.
  
  
• Chronic bloody diarrhea. This may be a symptom of inflammatory bowel disease (IBD), especially if accompanied by abdominal pain, cramping and unintentional weight loss.
  
  
• Chronic oily or fatty diarrhea (stool often appears bulky, greasy or foul smelling). This may indicate absorption problems or other digestive problems. It may also indicate pancreatitis, bile duct or liver diseases, celiac disease or complications of intestinal surgery.

In some cases, patients may pass more than a quart of stool each day. Passing large volumes of diarrhea can lead to dehydration, as the body loses significant amounts of water and salt. Dehydration can be life-threatening for the very young, the elderly and people with weakened immune systems.

Signs and symptoms of dehydration in adults include:

• Thirst
• Dry mouth and/or skin
• Fatigue
• Decreased and/or dark-colored urine
• Feeling faint or dizzy
• Low blood pressure
• Eyes that appear sunken

Adults with diarrhea should contact their physician when they become dehydrated or when they experience any of the following:

• Diarrhea for three or more days
• Severe pain in the abdomen or rectum
• Temperature of 102 degrees Fahrenheit (34 degrees Celsius) or higher
• Blood in stool or black, tar-like stool

Infants and children are especially vulnerable to dehydration. Infants can become dehydrated after just one or two days of severe diarrhea. Signs of dehydration in children include:

• Dry mouth or tongue
• Lack of tears when crying
• No wet diapers for three or more hours
• Sunken abdomen, eyes or cheeks
• High fever
• Restlessness, irritability
• Skin that does not flatten after being pinched and released

Diarrhea can be either short-term (acute) or long-term (chronic) in duration. Almost everyone experiences the severe and sudden development of acute diarrhea at some point in their lives. It is usually short-lived (a few days) and may run its course without the need for medication. Acute diarrhea is most often caused by infection (infectious diarrhea), and may also be a side effect of many different prescription or over-the-counter medications.

Chronic diarrhea, on the other hand, lasts for at least four weeks and may indicate a more serious problem that requires treatment. Irritable bowel syndrome (IBS) is the most common cause of chronic diarrhea in the United States.

Diarrhea can be categorized into different types, depending on the processes that drive it. For example, the rapid transit of stool through the digestive tract is responsible for diarrhea that occurs with motility disorders such as IBS. Food that passes too quickly through the intestines or in too large an amount to be properly absorbed is a common cause of diarrhea. Additional types of diarrhea by process include:

• Osmotic diarrhea. Occurs when sugars (e.g., lactose, fructose), sugar alcohols (e.g., sorbitol) and some minerals (e.g., magnesium, sulfate, phosphate) in the intestines fail to be absorbed into the body. These unabsorbed substances draw water into the intestines, causing watery stool. Diarrhea caused by lactose intolerance is an example of osmotic diarrhea. Sorbitol is also a common cause of this type of diarrhea. Typically, osmotic diarrhea goes away when foods containing these elements are removed from a patient’s diet.
  
  
• Secretory diarrhea. Occurs when the intestines release water and salt into the stool, making it runny. This can be due to numerous causes, the most common being infections that release toxins. The toxic substances interfere with the intestines, causing them to secrete water and salt. Carcinoid tumors can also stimulate secretions that lead to secretory diarrhea. Secretory diarrhea can be due to poor absorption of bile acids and fatty acids by the intestines. This may occur in people with certain medical conditions, such as celiac disease and inflammatory bowel disease (IBD).
  
  Patients with a digestive system that moves digestive products too quickly are also prone to secretory diarrhea, because the intestines do not have enough time to absorb fluid. Secretory diarrhea usually continues even if a person fasts.
  
  
• Exudative diarrhea. When inflammation or irritation of the lining of the colon causes the release of blood, mucus or other fluids. This type of diarrhea can be caused by a number of conditions (e.g., IBD, tuberculosis, some cancers).  

It is important to note that different types of diarrhea may occur at the same time. For example, it is rare that patients who see a physician about their diarrhea have solely osmotic or solely secretory diarrhea. Some viral or inflammatory conditions can cause both to occur simultaneously.

Paradoxical diarrhea is the appearance of diarrhea-like symptoms when the cause is actually a complication of constipation called a fecal impaction. In patients with paradoxical diarrhea, liquid stool flows around hard, impacted stool still inside the rectum, giving the false impression of diarrhea. Paradoxical diarrhea most commonly occurs in children, the elderly or adults with limited mobility or mental capacity.

Diarrhea can be a symptom of many different illnesses and medical conditions, or a side effect of certain medications. Diarrhea may also be the result of specific dietary choices. Potential causes of diarrhea include:

• Viral infection. Viruses are the most common cause of infectious diarrhea. A virus may damage the lining of the small intestine, interfering with normal fluid and nutrient absorption, causing diarrhea. Rotavirus is the most common cause of severe diarrhea in children – an estimated 55,000 children are hospitalized for it each year in the United States, according to the Centers for Disease Control and Prevention (CDC). Viral infections can spread easily. Noroviruses cause gastroenteritis and intestinal flu, which include diarrhea as a primary symptom.
  
  
• Bacteria/parasites. Bacteria (e.g., Escherichia coli, salmonella) and parasites (e.g., giardia) are commonly ingested through contaminated food or water. Some bacteria and parasites release toxins that cause the intestines to secrete water and salt, adding to the liquidity of stool.
  
  
• Intestinal disorders. If the colon is inflamed or diseased, it may be unable to absorb fluid from food products traveling through the intestines, resulting in diarrhea. Examples of intestinal disorders that can cause diarrhea include inflammatory bowel disease (IBD), celiac disease and dysentery.
  
  
• Motility disorders. Problems with the movement of stool through the digestive tract can also lead to diarrhea. When stool moves too quickly through the intestines, not enough fluids are absorbed from the stool, leading to watery, unformed bowel movements. If stool moves too slowly, it can lead to bacteria overgrowth and loose, greasy bowel movements. Causes of motility disorders include an overactive thyroid, irritable bowel syndrome (IBS), scleroderma and antacids that include magnesium. Stress and anxiety can also cause increased movement of stool through the digestive tract, resulting in diarrhea.
  
  
• Surgical procedures. Various types of surgery may cause changes within the digestive tract that can lead to diarrhea. Diarrhea can be caused by dumping syndrome, a common consequence of gastric surgery. Bowel resections decrease surface area of the intestines, which limits fluid absorption and may cause diarrhea. Bacterial overgrowth as a result of Crohn's Disease or intestinal surgery can cause inflammation and diarrhea. Surgery to remove the gallbladder can speed the movement of stool through the intestines, causing diarrhea, but this is usually temporary.
  

• Medication. There are hundreds of prescription and over-the-counter medications that can cause diarrhea. Antibiotics are the most common culprit – they can disrupt the natural balance of bacteria in the intestines. Diarrhea is also a common side effect of medications used to treat depression, high blood pressure and cancer. Drugs and synthetic foods used to promote weight loss (e.g., foods containing the fat substitute olestra) often cause diarrhea. Habitual use of laxatives can also cause diarrhea. Research also indicates that use of illegal drugs (e.g., crack cocaine) can cause diarrhea as well. In most cases, diarrhea resolves once the antibiotic or other aggravating agent is discontinued.
  
  
• Artificial sweeteners. Products used as sugar substitutes, such as sorbitol, are sometimes not absorbed into the bloodstream and remain in the intestines, leading to loose, watery stool.
  
  
• Caffeine, alcohol. Caffeine and alcohol stimulate the passage of stool, which can cause it to move too quickly through the intestines, disrupting normal fluid absorption and resulting in watery stool.
  
  
• Lactose intolerance. People who lack the enzyme lactase are unable to digest milk products. The undigested lactose in the intestines causes an osmotic diarrhea (diarrhea caused by problems with the absorption of carbohydrates).
  
  
• Ingestion of toxins. The inadvertent ingestion of environmental toxins (e.g., insecticides, arsenic) can lead to diarrhea. Eating poisonous mushrooms may also cause diarrhea.

Physicians often rely on a patient’s report of symptoms in diagnosing the cause of and determining treatment for diarrhea. A medical history will include questions about the duration and severity of symptoms, eating habits and current medications. A physical examination will allow a physician to look for signs of illness that may be causing the diarrhea.

Most people with diarrhea will not need extensive testing. When diarrhea goes away by itself, it is not usually necessary to submit to various tests to determine its cause. When tests are used, they may include:

• Stool tests. Stool is tested for bacteria, parasites or other signs of infection that may be causing the diarrhea.
  
  
• Blood tests. Blood is drawn and tested for evidence of disease that may be causing the diarrhea.
  
  
• Fasting tests. Patients are asked to avoid certain products to determine whether an allergy or food intolerance may be responsible for the diarrhea. Bowel habits are observed to identify whether a change in diet affects the diarrhea. Physicians commonly ask patients to avoid dairy products, carbohydrates and wheat, although other foods may be included. Milk may be purchased with added lactase, and yogurt is usually well tolerated.
  
  
• Endoscopy. A flexible tube (with attached light and camera) is inserted into a patient’s digestive tract to identify any abnormalities that may be causing the diarrhea. Biopsies and color photographs may be taken during this procedure. The tube is inserted via the anus and usually through the entire colon in a colonoscopy. A sigmoidoscopy is similar, but only involves the lower part of the colon (the sigmoid colon).

Dehydration is a serious consequence of diarrhea that should be addressed immediately. Replacement of fluids and electrolytes is required for patients who suffer from dehydration. Sports drinks, which include sodium and potassium, can help restore fluid balance and cardiovascular functioning in the body. Other fluids used to replenish the body after dehydration include fruit drinks, tea, broth and carbonated beverages that have gone flat (contain no fizz). Intravenous rehydration may be necessary for infants or the elderly who are profoundly dehydrated.

In general, treatment for diarrhea will depend on its cause. Diarrhea caused by a viral infection will not respond to antibiotics and will most likely resolve on its own within 24 to 48 hours, depending on the severity of the diarrhea. If diarrhea is the result of invasive bacteria, such as salmonella, antibiotics are sometimes used – especially for patients with compromised immune systems or cardiovascular problems. For chronic diarrhea that is the result of intestinal disorders, specific medical treatment of those disorders may be required.

Many cases of diarrhea can be resolved through changes to diet. Removing alcohol or caffeine products from the diet, for example, may relieve some forms of chronic diarrhea. Dairy products and foods high in fat are other foods that, if removed or limited in a patient’s diet, can help relieve diarrhea. On the other hand, bananas, pears and boiled or mashed potatoes are good sources of potassium, which may be depleted in a person with diarrhea. Adding these food products to a patient’s diet can help restore the balance of nutrients.

In addition, certain prescription and over-the-counter medications (antidiarrheals) can help stop diarrhea. These include:

• Adsorbents. These medications bind fluids to them, helping stool to be less watery. Adsorbents used to stop diarrhea include bismuth subsalicylate, kaolin and pectin. Patients should check with their physician before using adsorbents, since they may interfere with other medications being taken. In addition, use of certain adsorbents may change stool color to black.
  
  
• Anti-motility medications. Slows down the contractions of intestinal muscles so that stool travels more slowly through the digestive tract, allowing more fluid to be absorbed by the intestines. Patients should check with their physician before using anti-motility medications to treat diarrhea. If diarrhea is caused by infection, these medications may trap bacteria in the intestines, prolonging the problem.

A change in diet is one of the easiest ways to prevent diarrhea. Certain food products can aggravate or cause diarrhea, whereas others can help prevent it. Paying attention to what is consumed and limiting some choices while seeking out others, can help prevent diarrhea.

The first step is to avoid those foods or drinks that can cause diarrhea, such as:

• Fatty foods. A diet high in fats (e.g., fried foods, pastries, potato chips) can lead to absorption problems in the intestines, making stool soft and greasy.
  
  
• High-fiber foods. Fiber in foods such as bran, beans, fresh fruits and vegetables can add bulk and softness to stool, aggravating diarrhea.
  
  
• Caffeine, alcohol. Alcohol or products containing caffeine (e.g., coffee, soda) can stimulate the passage of stool through the intestines, causing insufficient fluid absorption and diarrhea.
  
  
• Dairy products. An inability to digest lactose in dairy products can increase the wateriness of stool and lead to diarrhea.
  
  
• Unpasteurized products. Products that are not pasteurized (e.g., some cheeses) may contain bacteria that, once consumed, may cause diarrhea.

Patients will also want to gradually add foods or drinks to their diet that can help prevent diarrhea. This includes soft, easily digested foods (e.g., soup, crackers) as well as low-fiber foods (e.g., rice, noodles, white bread, lean meats). The American Dietetic Association recommends the BRAT (banana, rice, applesauce, toast) diet to help prevent overstimulation of the intestines and to help reduce the frequency of bowel movements. Researchers are currently studying whether consumption of probiotic foods (foods that contain good bacteria) can help prevent diarrhea.

For chronic diarrhea caused by an underlying intestinal disorder, such as irritable bowel syndrome (IBS), specific dietary changes may be recommended.

Practicing good hygiene is another way to prevent diarrhea caused by bacterial or viral infection. This includes washing hands with soap and water before eating, when preparing food, after using the bathroom and after coming into contact with surfaces that can harbor diarrhea-causing bacteria (e.g., computer keyboards).

When severe diarrhea is caused by ingesting contaminated food or water while in a foreign country, it is called traveler's diarrhea. This is usually only a problem when visiting developing countries. Visitors to developed nations, such as the United States, Canada, Japan, Australia, New Zealand and most of Europe, are less likely to contract traveler’s diarrhea.

People can lower their risk of infectious diarrhea when traveling.  Patients may receive antibiotics in advance from their physician, depending on the location and duration of travel. In addition, traveler’s diarrhea can be avoided by taking the following actions:

• Eat only hot, well-cooked foods. Avoid food that has been left at room temperature for long periods of time. Meat or shellfish should be hot when served and consumed – do not consume raw or rare meat or fish. Avoid food sold by street vendors.
  
  
• Avoid accidental exposure to contaminated water. Use bottled water when traveling. Avoid ice and tap water, even when brushing teeth, to avoid possible contaminants in the water. Do not let shower water get into the ears or mouth.
  
  
• Choose hot beverages or those in sealed containers. Bottled water, carbonated soft drinks, hot coffee and tea are safe to drink.
  
  
• Avoid raw fruits or vegetables, unless they can be peeled. Fruits or vegetables may have been rinsed with contaminated water.
  
  
• Avoid unpasteurized products. Milk, orange juice or other products that have not been pasteurized (heated during processing to eliminate bacteria), may cause diarrhea.

Overuse of antibiotics should be avoided. Antibiotics are a common cause of diarrhea, since they upset the natural balance of bacteria in the intestines. By avoiding the unnecessary use of antibiotics, a patient can help prevent diarrhea.

Research also shows that breastfeeding infants may help reduce their risk of developing diarrhea. In addition, two new vaccines have recently been developed to prevent infants and children from getting rotavirus, a leading cause of diarrhea in this population.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following diarrhea-related questions:

1. Is it normal to have diarrhea? How often is normal?
   
   
2. Should I be concerned about the frequency of my bowel movements?
   
   
3. Is watery stool the only way to tell if I have diarrhea?
   
   
4. When should I seek treatment for diarrhea?
   
   
5. What do you think is the cause of my diarrhea?
   
   
6. Should I be screened for any conditions or potential causes?
   
   
7. What type of medication used to treat diarrhea is appropriate for me?
   
   
8. Are there medications or home remedies you can recommend to help with the other symptoms associated with my diarrhea (e.g., stomach pain)?
   
   
9. What diet or lifestyle changes can I make to help relieve my diarrhea?
   
   
10. During treatment, are there any side effects or changes that you want me to report to you immediately?