Diarrhea is an increase in the volume, wateriness, or frequency of bowel movements.
The frequency of bowel movements alone is not the defining feature of diarrhea. Some people normally move their bowels 3 to 5 times a day. People who eat large amounts of vegetable fiber may produce more than a pound (1/2 kilogram) of stool a day, but the stool in such cases is well formed and not watery.
Diarrhea is often accompanied by gas, cramping, an urgency to defecate, and, if the diarrhea is caused by an infectious organism or a toxic substance, nausea and vomiting.
(See also Diarrhea in Children.)
Complications
Diarrhea can lead to dehydration and a loss of electrolytes, such as sodium, potassium, magnesium, chloride, and bicarbonate, from the blood. If large amounts of fluid and electrolytes are lost, the person feels weak, and blood pressure can drop enough to cause fainting (syncope), heart rhythm abnormalities (arrhythmias), and other serious disorders. At particular risk are people who are very young, very old, or weakened and people with very severe diarrhea.
Causes of Diarrhea
There are many different causes of diarrhea, depending on how long the diarrhea has lasted (see table Some Causes and Features of Diarrhea).
The most common causes of acute diarrhea (lasting less than 4 days) are
Infection with viruses, bacteria, or parasites (gastroenteritis)
Side effects of a medication
The most common causes of chronic diarrhea (lasting more than 4 weeks) are
Side effects of a medication
Diarrhea that has been present for more than 4 weeks may be a lingering case of acute diarrhea or the early stage of a disorder that causes chronic diarrhea.
Classification
Normally, stool is 60 to 90% water. Diarrhea occurs when not enough water is removed from the stool, making the stool loose and poorly formed. Stool may contain too much water if it
Passes too quickly through the digestive tract
Contains certain substances that prevent the large intestine from absorbing water
Contains excess water secreted by the intestines
Rapid passage (transit) of stool is a common cause of diarrhea. For stool to have normal consistency, it must remain in the large intestine for a certain amount of time. Stool that leaves the large intestine too quickly is watery.
Many medical conditions and treatments can decrease the amount of time that stool stays in the large intestine:
An overactive thyroid (hyperthyroidism)
Zollinger-Ellison syndrome (a condition of over-production of acid by a tumor)
Surgical removal of part of the stomach, small intestine, or large intestine or of the gallbladder (cholecystectomy)
Surgical bypass of part of the intestine
Inflammatory bowel disease (such as ulcerative colitis)
Medications such as antacids containing magnesium, laxatives, prostaglandins, serotonin, and even caffeine
Many foods, especially those that are acidic or have a very high amount of sugar (such as waffle or maple syrup), can increase the rate of transit (see table Foods and Beverages That May Cause Diarrhea). Some people are intolerant of specific foods and always develop diarrhea after eating them.
Stress and anxiety are also common causes.
Osmotic diarrhea occurs when certain substances that cannot be absorbed through the colon wall remain in the intestine. These substances cause excessive amounts of water to remain in the stool, leading to diarrhea.
Certain foods (such as some fruits and beans) and sugar substitutes in dietetic foods, candy, and chewing gum (for example, hexitols, sorbitol, and mannitol) can cause osmotic diarrhea.
Lactase deficiency also can lead to osmotic diarrhea. Lactase is an enzyme normally found in the small intestine that converts lactose (milk sugar) to glucose and galactose, so that it can be absorbed into the bloodstream. When people with lactase deficiency drink milk or eat dairy products, lactose is not digested. As lactose accumulates in the intestine, it causes osmotic diarrhea—a condition known as lactose intolerance. The severity of osmotic diarrhea depends on how much of the osmotic substance is consumed. Diarrhea stops soon after the person stops eating or drinking the substance.
Blood in the digestive tract also acts as an osmotic agent and results in black, tarry stools (melena).
Another cause of osmotic diarrhea is an overgrowth of normal intestinal bacteria or the growth of bacteria normally not found in the intestines.
Antibiotics can cause osmotic diarrhea by destroying the normal intestinal bacteria (see, for example, Clostridioides difficile–induced colitis).
Secretory diarrhea
Certain toxins—such as the toxin produced by a cholera infection or during some viral infections—can cause these secretions. Infections by certain bacteria (for example, Campylobacter) and parasites (for example, Cryptosporidium) can also stimulate secretions. The diarrhea can be massive—more than 1 quart (1 liter) of stool an hour in cholera.
Other substances that cause salt and water secretion include certain laxatives, such as castor oil, and bile acids (which may build up after surgery to remove part of the small intestine).
Certain rare tumors, such as carcinoid tumors, gastrinomas, and VIPomas, also can cause secretory diarrhea, as can some polyps.
Inflammatory diarrhea occurs when the lining of the large intestine becomes inflamed, ulcerated, or engorged and releases proteins, blood, mucus, and other fluids, which increase the bulk and fluid content of the stool. This type of diarrhea can be caused by many diseases, including ulcerative colitis, Crohn disease, tuberculosis, and cancers such as lymphoma and adenocarcinoma. When the lining of the rectum is affected, people often feel an urgent need to move their bowels and have frequent bowel movements because the inflamed rectum is more sensitive to expansion (distention) by stool.
Diarrhea caused by malabsorption is characterized by oil or grease in the stool and an oily rim around the toilet bowl after stool is flushed. Malabsorption of bile salts, which can result from certain disorders, can cause diarrhea by stimulating water and electrolyte secretion. The stools have a green or orange color.
Foods and Beverages That May Cause Diarrhea
Food or Beverage | Ingredient Causing Diarrhea |
|---|---|
Sugar-free gum, mints, sweet cherries, or prunes | Hexitols, sorbitol, or mannitol |
Apple juice, pear juice, grapes, honey, dates, nuts, figs, soft drinks (especially fruit flavors), prunes, or waffle or maple syrup | Fructose |
Milk, ice cream, yogurt, or soft cheese | Lactose |
Coffee, tea, cola drinks, or some over-the-counter headache remedies | Caffeine |
Evaluation of Diarrhea
Not every episode of diarrhea requires immediate evaluation by a doctor. The following information can help people decide whether a doctor’s evaluation is needed and help them know what to expect during the evaluation.
Warning signs
Certain findings raise suspicion of a more serious cause of diarrhea.
Blood or pus in the stool
Fever
Signs of dehydration (such as decreased urination, lethargy or listlessness, extreme thirst, and a dry mouth)
Chronic diarrhea
Diarrhea at night
Weight loss
When to see a doctor
People who have warning signs of blood or pus in the stool, fever, or signs of dehydration should see a doctor right away, as should those with significant abdominal pain. Such people may need immediate testing, treatment, and sometimes admission to a hospital.
If the only warning signs are chronic or nighttime diarrhea or weight loss, people should see a doctor within a week or so.
People without warning signs should call a doctor if diarrhea lasts for more than 72 hours. Depending on the person's other symptoms, age, and medical history, the doctor may recommend the person have an examination or try at-home or over-the-counter treatments (see treatment of diarrhea).
What the doctor does
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the diarrhea and the tests that may need to be done (see table Some Causes and Features of Diarrhea).
A doctor begins by asking how long the diarrhea has been going on, how severe it has been, and whether friends, family members, or other personal contacts currently have diarrhea too.
Other important questions are focused on the following:
Circumstances around when it started (including recent travel, food ingested, and source of water)
Medication use (including any antibiotics within the previous 3 months)
Abdominal pain or vomiting
Frequency and timing of bowel movements
Changes in stool characteristics (for example, presence of blood, pus, oil or grease, or mucus and changes in color or consistency)
Changes in weight or appetite
Feeling an urgent need to defecate or to defecate constantly
The physical examination begins with the doctor's evaluation of the person's fluid and hydration status. A full examination of the abdomen is done, as is a digital rectal examination to check for the presence of blood.
Some Causes and Features of Diarrhea
Cause | Common Features* | Tests |
|---|---|---|
Acute (less than 4 days)† | ||
Gastroenteritis due to viruses, bacteria, or parasites‡ | Often vomiting Rarely fever or blood in stool Little or no abdominal pain (except during vomiting) Sometimes recent contact with infected people (such as those at a day care center, at a camp, or on a cruise), with animals at a petting zoo (where Escherichia coli [E. coli] may be acquired), or with reptiles (where Salmonella bacteria may be acquired) Sometimes recent consumption of undercooked, contaminated food or contaminated water | A doctor’s examination Sometimes examination and testing of stool |
Diarrhea that started suddenly, often with vomiting, within 4 to 8 hours of eating contaminated food Often present in other people Typically lasting 12 to 24 hours | A doctor’s examination | |
Side effects of medications‡ (including antibiotics, many cancer chemotherapy agents, colchicine, and quinine/quinidine) | Recent use of a medication that causes diarrhea Often no other symptoms | A doctor’s examination Sometimes tests for Clostridioides difficile (sometimes called C. diff) toxin in stool |
Chronic (4 weeks or more) | ||
Dietary factors such as
| Diarrhea only after consuming a substance that could cause diarrhea Abdominal bloating and passing of gas (flatulence) Explosive diarrhea | A doctor’s examination Sometimes a breath test to detect hydrogen, indicating undigested food Examination and analysis of stool to check for unabsorbed carbohydrates |
Intermittent diarrhea associated with abdominal pain Often diarrhea alternating with constipation No bleeding, weight loss, or fever Usually begins during adolescence or the 20s Symptoms usually present for more than 12 weeks Changes in the frequency of bowel movements or consistency of stool | A doctor’s examination Sometimes blood tests and colonoscopy | |
Inflammatory bowel disease such as | Blood in stool, crampy abdominal pain, weight loss, and loss of appetite Sometimes arthritis, rashes, sores in the mouth, and tears in the rectum | Colonoscopy CT or MRI Stool tests |
Malabsorption disorders such as
| Light-colored, soft, bulky, and unusually foul-smelling stool that may appear oily Abdominal bloating and flatulence Weight loss For tropical sprue, long-term (over 1 month) residence in a tropical country For pancreatic insufficiency, usually in a person known to have a disorder of the pancreas (such as chronic pancreatitis or cystic fibrosis) | Tests to measure the amount of fat in stool samples collected over several days If celiac disease is suspected, blood tests to measure the antibodies produced when people with celiac disease eat foods containing gluten For celiac disease and tropical sprue, especially celiac disease, biopsy of the small intestine |
Certain tumors
| For colon cancer, sometimes blood in stool, decreased stool diameter, and weight loss For endocrine tumors, various symptoms, including abdominal pain or cramping, flushing, and massive watery diarrhea | Blood tests Colonoscopy |
Often nervousness, trouble tolerating a hot environment, fatigue, palpitations, weight loss, and rapid heart rate | Blood tests | |
Surgery on the stomach or intestines (such as gastric bypass for weight loss or removal of a significant length of intestine) | Obvious recent surgery | A doctor’s examination |
* Features include symptoms and the results of the doctor's examination. Features mentioned are typical but not always present. | ||
† Diarrhea that has been present for 1 to 4 weeks may be a lingering case of acute diarrhea or the early stage of a disorder that causes chronic diarrhea. | ||
‡ Certain infections and certain medications can also cause chronic diarrhea. | ||
CT = computed tomography; HIV = human immunodeficiency virus; MRI = magnetic resonance imaging. | ||
Testing
The need for testing depends on what the doctor finds during the history and physical examination (see table Some Causes and Features of Diarrhea).
Acute watery diarrhea (lasting less than about 4 days) without warning signs is usually caused by a viral infection, and people who otherwise appear well do not require testing. People with acute diarrhea who have warning signs of dehydration, bloody stool, fever, or severe abdominal pain typically need testing—particularly those who are very young or very old. In these people, doctors do blood tests to detect blood and electrolyte abnormalities and stool tests to detect blood, markers of inflammation, and the presence of infectious organisms (such as Campylobacter, Yersinia, amebas, Giardia, and Cryptosporidium). Some causes of infection are detected by looking under the microscope, whereas others require a culture (growing the organism in the laboratory) or special enzyme tests (for example, Shigella or Giardia). If the person has taken antibiotics within the past 2 to 3 months, the doctor may test the stool for Clostridioides difficile (C. diff) toxin. A colonoscopy is usually not necessary.
For diarrhea lasting more than 4 weeks (more than 1 to 3 weeks for people who have a weakened immune system or who appear seriously ill), similar tests are done. In addition, the doctor may test the stool, including tests for fat (indicating malabsorption), do blood tests, and do a colonoscopy to examine the lining of the rectum and colon and to gather samples to test for infection. People whose symptoms seem related to diet may have a breath test to look for hydrogen, which suggests they are not absorbing carbohydrates. Sometimes a biopsy (removal of a tissue specimen for examination under a microscope) of the rectal lining is done to look for inflammatory bowel disease. Sometimes the volume of stool over a 24-hour period is determined. Imaging tests, such as computed tomography (CT) enterography, may be needed if the doctor suspects certain tumors. If doctors are still uncertain about the diagnosis, they may need to assess the function of the pancreas. Depending on the person's symptoms, doctors may also do tests for thyroid or adrenal gland disorders.
Treatment of Diarrhea
Treatment is directed at the cause of diarrhea, when possible. For example, foods and medications that cause diarrhea are avoided, tumors are removed, and medications are given to eradicate a parasitic infection. However, in many cases, the body heals itself. A viral cause usually resolves by itself in 24 to 48 hours.
(See also Treatment of Diarrhea in Children.)
Dehydration
Extra fluids containing a balance of water, sugars, and salts are needed for people who are dehydrated. As long as the person is not vomiting excessively, these fluids can be given by mouth (see Treatment of Dehydration).
Seriously ill people and those with significant electrolyte abnormalities require intravenous fluids and sometimes hospitalization.
Medications
Salmonella, Shigella, and Clostridioides difficile, can be worsened by antidiarrheal medications. Doctors typically recommend antidiarrheal medications only for people with watery diarrhea and no warning signs because such people are unlikely to have such bacterial infections.
Over-the-counter medications include adsorbents (for example, kaolin-pectin), which adhere to chemicals, toxins, and infectious organisms. Some adsorbents also help firm up the stool. Bismuth helps many people with diarrhea. It has a normal side effect of turning the stool black.
Key Points
In people with acute diarrhea, doctors examine the stool only if they suspect people have certain acute infections or if people have prolonged symptoms (that is, more than about 4 to 7 days) or warning signs.
Doctors avoid using antidiarrheal medications if there is a possibility that the person has Clostridioides difficile, Salmonella, or Shigella.
