Common causes of diarrhea

Few things are more urgent than the need to go to the bathroom. Unfortunately, diarrhea can result in urgency, and it can also send someone running to the bathroom multiple times. It is often accompanied by abdominal cramping or a stomachache. Diarrhea is one of the most commonly reported illnesses in the U.S.

The causes behind diarrhea, however, are varied. Runny bowels may be caused by something as simple as diet. It may also be a symptom of an intestinal condition, such as inflammatory bowel syndrome (IBS), ulcerative colitis or other causes of varying severity.

Thankfully, most cases of diarrhea go away within a couple days. Even persistent and chronic types can often be managed with appropriate options, so it's important to talk to a health care provider.

Learn about the common causes of diarrhea and how to help identify what’s causing those loose, watery bowel movements.

In this article:

Diarrhea: definition and impact

Diarrhea is having three or more loose, watery stools in a day. It can be acute, persistent or chronic. Diarrhea can have a massive impact on life and productivity. It can also lead to malnutrition — and in the worst case, death.

Common causes of acute diarrhea

Acute diarrhea is a sudden bout of loose, watery stools that lasts no longer than seven days.

It’s the most common type of diarrhea and typically can be managed with over-the-counter (OTC) anti-diarrheal medicines, like loperamide and bismuth subsalicylate. Be sure to check with a health care provider before taking antidiarrheal medications for acute diarrhea.

The most common acute diarrhea causes include:

Infectious agents

Infections (such as viral gastroenteritis) are one of the most common causes of acute diarrhea. Some viral infections include rotavirus, which can cause watery diarrhea and vomiting in children, and norovirus, the leading cause of vomiting, diarrhea and foodborne illness in the U.S. 

Parasitic and bacterial infections can also cause acute diarrhea. People can also get infections from food poisoning, which happens when bacteria and parasites enter the body through contaminated food and water.

Medication side effects

Antibiotics, antacids that contain magnesium and even certain cancer treatments can trigger acute diarrhea. Some liquid medicines include sugar alcohols (such as sorbitol, mannitol and xylitol), which can also cause diarrhea for some people.

Common causes of chronic diarrhea

Diarrhea is typically defined by the passage of 3 or more loose (or liquid) stools per day. Doctors may also diagnose someone with diarrhea if they are passing more stool than usual. Acute diarrhea typically lasts less than 7 days. Persistent or prolonged diarrhea can last anywhere from 2 weeks to 29 days. If the condition lasts 30 days or more, it is considered chronic.

Unlike acute diarrhea, chronic diarrhea tends to be noninfectious, is less likely to go away on its own and often requires a diagnosis. This type of diarrhea is often classified into three types:

• Fatty or malabsorptive: characterized by excess gas, steatorrhea or weight loss.
• Inflammatory: typically identified by blood and pus in the stool.
• Watery: related to conditions like irritable bowel syndrome and microscopic colitis.

Some of the most common chronic diarrhea causes include the following:

Irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common condition thought to affect 10 to 15 percent of adults in the U.S. It may cause bloating, stomach pain or discomfort, and changes in bowel movement. While IBS causes symptoms, there are no signs of disease or damage in the gut.

IBS can cause diarrhea, constipation or a combination of both. If someone has IBS-D, also called diarrhea-predominant IBS, more than a quarter of their stool is loose or watery, and less than a quarter are hard or lumpy.

Inflammatory bowel disease

Inflammatory bowel diseases (IBD) are conditions that cause recurring inflammation and damage to the intestinal tract. In IBD, the immune system mistakenly attacks healthy bowel cells, causing irritation and ulcers (open sores) on the gut lining. Look for these symptoms of IBD:

• Diarrhea or change in bowel movements
• Fatigue
• Nausea
• Stomach pain
• Unintended weight loss

The main types of IBD are Crohn’s disease and ulcerative colitis.

In Crohn's disease, inflammation can affect all layers of the intestinal wall and any part of the digestive tract, including the small and large intestines. A few common symptoms are diarrhea, abdominal pain and weight loss. However, a person's symptoms may come in waves and vary depending on which part of the body is affected and how severe the damage is.

Ulcerative colitis is the most common type of IBD. It affects the inner lining of the colon and rectum. Some symptoms that are seen in ulcerative colitis, but not typically seen with other types of IBD are abdominal cramping with bowel movements and stool with mucus or blood. In contrast to Crohn’s disease, which has patchy areas of inflammation with sections of healthy gut in between, the inflammation in ulcerative colitis is widespread and continuous.

Celiac disease

Celiac disease is an autoimmune condition affecting the small intestine. It is triggered by gluten consumption. Consuming gluten may lead to digestive symptoms or even symptoms in other parts of the body.

Lactose intolerance

Lactose intolerance may cause abdominal pain, diarrhea and gas after eating foods or liquids containing lactose, a sugar naturally found in milk products. The condition happens when the small intestine makes low amounts of an enzyme called lactase, which is required to break down the lactose. A person with lactose intolerance will typically experience symptoms within a few hours after consuming products with lactose.

Microscopic colitis

Microscopic colitis is a type of IBD that causes inflammation in the inner lining of the colon. It most commonly causes chronic watery, nonbloody diarrhea. Doctors can complete a colonoscopy with a biopsy to collect small pieces of tissue from the lining of someone's colon. To help diagnose microscopic colitis, the tissue sample will then be examined under a microscope to check for signs of the disease.

Anyone can develop microscopic colitis, but it’s more common in older adults. It may be three to nine times more common in women. (For the purposes of this article, “women” refers to biological sex.)

Dietary causes of diarrhea

People who get diarrhea frequently may eventually uncover a food allergy or a problem digesting certain carbohydrates or proteins. Health care providers can advise on how to handle these challenges. But food can contribute to more temporary instances of diarrhea as well.

Health care providers may recommend avoiding things like alcoholic beverages, fried foods and certain soft drinks when experiencing acute diarrhea. The list doesn’t end there, either. Here are some other items that might make symptoms worse:

• Foods and drinks with high amounts of simple sugars (e.g., fructose, lactose) found in some sweetened beverages, fruit juices, candies and packaged desserts
• High-fat foods such as pizza and fast food
• Milk and dairy products containing lactose, which can be particularly problematic for some individuals recovering from acute diarrhea
• Products containing sugar alcohols, commonly found in sugar-free gum and candies

Another food grouping that can cause diarrhea are the FODMAPs, which stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols. FODMAPs are short-chain carbohydrates that the digestive tract can’t fully digest and absorb. They can cause excessive gas production. This can lead to symptoms of bloating and diarrhea. FODMAPs are not unhealthy or harmful, but they may increase diarrhea symptoms in people already sensitive to diarrhea.

Traveler’s diarrhea

Traveler’s diarrhea may happen when someone visits places where food and water may be contaminated. While it can happen anywhere, more cases occur in certain higher-risk regions.

Help reduce the risk of getting traveler’s diarrhea by introducing these measures into a travel routine:

• Avoid ice.
• Avoid street food or food sitting in a buffet.
• Avoid using tap water for drinking or brushing teeth.
• Frequently wash hands with soap and water or use an alcohol-based sanitizer if water and soap are unavailable.
• Only eat foods that are served hot and fully cooked.
• Opt for factory-sealed beverages.
• Thoroughly wash raw fruits and vegetables in clean water.

Diarrhea in children

Diarrhea is a very common problem affecting young children. It is also the third leading cause of death worldwide in children under 5 years old. Children can get acute diarrhea from schools and day care.

For mild diarrhea, children should be kept hydrated with enough fluids. For infants, it is recommended that caregivers continue with breast milk or formula.

Aside from adequate hydration, older children can be given oral rehydration solutions (ORS). Most children with mild diarrhea do not need electrolyte solutions. Fruit juices and soft drinks have the wrong amounts of sugar and salt needed to help rehydrate and can worsen the condition.

Do not try to make electrolyte solutions at home and consult with a health care provider for any questions. In cases of severe diarrhea, health care providers may need to administer fluids intravenously in a hospital.

Diarrhea in older adults

Older adults may develop GI problems from certain medications. Staying hydrated, serving low-fiber foods and sticking to several small meals a day can help get an older adult get their digestive function back to normal.

It’s also best to talk to a health care provider about what medications may be causing diarrhea. Antibiotics, for instance, may disturb the natural balance of bacteria in the intestines.

Some potentially serious causes of diarrhea

Diarrhea is often not a cause for concern. But sometimes, it can signify a more serious health issue. In some cases, chronic diarrhea can be a symptom of more serious conditions, such as these:

Pancreatic disorders

The pancreas creates digestive juices that digest food. If a person has conditions like pancreatitis or pancreatic cancer, they may experience diarrhea or an upset stomach and pass greasy, bad-smelling stools.

Hyperthyroidism

Diarrhea can also be a symptom of endocrine diseases like hyperthyroidism. This condition speeds up several bodily functions, which can cause gastrointestinal (GI) tract symptoms like diarrhea.

Colon cancer

A change in bowel habits can be one of the signs of colorectal cancer. Signs may include a change in bowel habits, such as diarrhea or constipation that lasts for more than a few days. Other symptoms may include cramping, blood in the stool and unexplained weight loss.

Diagnosing the cause of diarrhea

Most cases of diarrhea are self-limiting and don't need intervention. However, if it’s persistent or causing worrisome symptoms, a health care provider can help find the cause and provide people with the most appropriate treatment options.

They will use information from someone’s medical history, physical exam and test results to help determine the cause of their diarrhea.

Diarrhea may lead to dehydration. In adults, the symptoms of dehydration include:

• Dark-colored urine
• Dizziness
• Dry mouth
• Dry skin
• Feeling tired
• Feeling very thirsty
• Urinating and sweating less than usual

Dehydration can be mild, or it can be severe enough to be life-threatening. Get medical help right away if the symptoms also include:

• Confusion
• Fainting
• Lack of urination
• Rapid breathing
• Rapid heartbeat
• Shock

Medical history and physical examination

A health care provider may ask about symptoms, including the consistency, color, volume, frequency, and duration of bowel movements. They may also ask about the following:

• Contact with other people who are sick
• Foods and drinks someone has consumed
• Medications someone is taking
• Recent travel

They may also ask if anyone in the patient’s family has been diagnosed with celiac disease, IBS, IBD or food allergies and intolerances.

Then, a health care provider may perform a physical exam to look for other symptoms that may explain what’s causing diarrhea and check for complications like dehydration. The exam may include checking vital signs, examining the abdomen, doing a digital rectal exam and other relevant evaluations.

Medical tests

Stool tests

Health care providers may also order a stool test to check for parasitic or bacterial infections. This also allows them to check for blood and other signs of diseases. Patients will be given a container for catching their stool and storing it. They’ll also be given instructions on where to take the container for analysis.

Blood tests

Blood tests can help rule out certain diseases and disorders. They can also help detect other possible problems, such as dehydration. Health care providers will collect blood samples in-office and send them to a lab for testing.

Laboratory tests

Health care providers may also order additional tests specific to their suspected cause:

• Hydrogen breath tests measure the hydrogen in someone’s breath to see if they may have certain intolerances, such as lactose intolerance.
• Elimination tests work by seeing if eliminating specific foods helps relieve someone’s diarrhea.
• Endoscopies look at the inside of someone’s digestive tract to help find out possible causes of someone's diarrhea.

Understanding the root cause of diarrhea

The condition may sometimes persist, causing discomfort and disrupting daily activities. Sometimes, it can also be a warning sign of a more serious problem.

Identifying the root cause of diarrhea is crucial to help find the right treatment and to make dietary and lifestyle changes to help prevent its recurrence.