What Causes Diarrhea? 10 Things That Can Trigger Loose Bowel Movements

Contaminated food, chronic diseases, daily medications—find out what could be causing your diarrhea, and how to stay healthy.

Each year, people in the US get diarrhea about 179 million times, according to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)—that's a lot of loose, watery stool.

Most of us get diarrhea every once in a while and it only lasts a few days — doctors call that acute diarrhea. But, for some people, diarrhea makes a more regular appearance. Diarrhea that keeps coming back or lasts for more than 14 days is considered chronic diarrhea.

Most of the time, acute diarrhea happens because of bacteria, viruses, and other microbes that cause infection. Diarrhea caused by an infection usually comes on quickly and goes away in a few days.

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What Causes Acute Diarrhea?

Acute diarrhea has a quick onset of the problem. It is usually short-termed and responds to treatment. There can be several causes of acute diarrhea.


Most often, when people get acute diarrhea, it's commonly blamed on something they ate—and, in general, that's probably true. Food contamination is one of the main ways bacteria, viruses, and parasites make their way into your system to make you sick. Bacteria including E. coli, Salmonella, Campylobacter, Shigella, and Listeria have traditionally lurked in eggs, raw and undercooked meats and shellfish, unpasteurized milk, and raw vegetables. They can also be found in foods that have not been refrigerated well enough.

But "something you ate" doesn't necessarily mean there was bacteria in the food. Bacteria can make their way into your body in many different ways. "Let's say someone had a really bad infection and they used the bathroom and they didn't wash their hands," Rabia De Latour, MD, a gastroenterologist at NYU Langone tells Health. You can probably guess what comes next. You shake that infected hand and then you use your hands to eat.

Luckily avoiding diarrhea-causing bacteria is relatively simple. Most importantly, wash your hands before you eat. Also make sure all produce is carefully washed before you eat it and cook all meat, poultry, and fish thoroughly—and refrigerate anything you don't plan on eating right away.

Viral Infections

Viruses are another major culprit in causing acute diarrhea, and they make it into your body much in the same way as bacteria. "It's basically a bug that either contaminates the food you eat or you touch something and then you touch your face or your mouth and you swallow," Lisa Ganjhu, DO, a gastroenterologist at NYU Langone tells Health.

Norovirus is probably the most common of the diarrhea-causing viruses. Fortunately, these stomach bugs usually work their way out of your system in a few days—unfortunately, they cause some pretty gnarly symptoms, like vomiting and abdominal pain, along with diarrhea. Avoid viruses by washing your hands often, practicing smart food hygiene, and not sharing food or drinks with someone who's sick.


Parasites are small organisms that, like viruses and bacteria, can infect food and water and end up in your system after you've eaten—or imbibed—the wrong thing. You're more likely to get a parasite if you're traveling. You may find them in raw or undercooked fish as well as underdone beef and pork (another reason not to eat raw foods abroad). Common infectious parasites are Cryptosporidium, Entamoeba histolytica, and Giardia lamblia.

Some infections cause worse symptoms than others, so always get medical help if you notice blood in your stool or if the diarrhea lasts a long time, regardless of what you think the cause might be, says Dr. Drake.


Although scientists don't know why it happens, there's lots of anecdotal evidence of the running poops. "Runner's diarrhea" as it's called, has many potential causes. "It's thought to be that if you're running hard you're moving blood away from your colon, and that can cause diarrhea," Dr. De Latour says.

According to the Mayo Clinic, other contributing factors could be that you're jostling your organs, that running changes intestinal hormone secretion, and that you have pre-race stress and anxiety. "What is clear is that food moves more quickly through the bowels of athletes in training," according to the Mayo Clinic.

What Causes Chronic Diarrhea?

Chronic diarrhea, on the other hand, typically isn't caused by infection. Chronic diarrhea can happen for many reasons, ranging from side effects of medications to symptoms of chronic disease. The good news is that regardless of the cause, most types of diarrhea can be treated or cured.

Food Intolerance

Depending on how quickly you catch a food intolerance, it can actually cause either acute or chronic diarrhea. Food intolerance is different from food poisoning or foodborne illness in that it's not a virus or bacteria causing a one-time bout of diarrhea.

Lactose intolerance is probably the most common kind of food intolerance—when you lack an enzyme necessary to process lactose, a sugar found in dairy products, drinking or eating milk, yogurt, or cheese can cause diarrhea. "Let's say you know you're lactose intolerant and someone accidentally puts milk in your coffee," Dr. De Latour says. One-time diarrhea that results from that would be acute diarrhea. But before you know that the milk in your daily coffee is causing frequent diarrhea, lactose intolerance leads to chronic diarrhea.

Most of the time, diarrhea caused by foods happens because of malabsorption, meaning you don't have enzymes to break down the food. "So the food is just passing right through," Dr. Ganjhu says.

Other possible food intolerances include intolerance to fructose (natural sugars in fruits and honey), sorbitol and mannitol (artificial sweeteners), and gluten. Celiac Disease, which is characterized as sensitivity to gluten is technically an autoimmune disease, but people who have Celiac often get diarrhea after having eaten gluten — a protein found in wheat, barley, and rye.

Although not technically a food intolerance, certain foods and drinks can also cause diarrhea if anyone drinks them in excess. "People who drink a lot of caffeine can get chronic diarrhea," Dr. De Latour says. Although it's not totally understood why we know that coffee gets bowels moving. Excess alcohol and excess liquorice can also lead to diarrhea.

Diarrhea and other symptoms should go away when you start to avoid any foods that are causing you trouble.

Irritable Bowel Syndrome

Irritable bowel syndrome—IBS, for short—is one of the most common causes of chronic diarrhea, according to Dr. Ganjhu. IBS is a gastrointestinal disorder that refers to a collection of symptoms often occurring together, including bloating, diarrhea, constipation, and general discomfort. Some people with IBS might have diarrhea more often, while others tend toward constipation, but more common still is to alternate between the two.

The causes of IBS remain mysterious but may be related to how the brain communicates with the gut and with changes in the balance of gut bacteria.

If you suspect IBS is causing your diarrhea, your doctor might suggest keeping a food diary and then tailoring your diet to avoid foods that trigger your symptoms. Certain medications can also help keep IBS at bay.

Inflammatory Bowel Disease

Inflammatory bowel disease, or IBD, is often confused with IBS, but it's a different entity altogether. Actually, it's two distinct entities, one being Crohn's disease and the other ulcerative colitis. In both conditions, the digestive tract becomes inflamed, reducing its ability to absorb and deliver nutrients. Most often, chronic inflammation from Crohn's disease affects the small intestine, Dr. Ganjhu says.

Ulcerative colitis, on the other hand, only targets the lining of the colon. Regardless, diarrhea is a symptom common to both. Experts aren't sure what causes the two conditions, but it looks like genetics and the immune system are involved, according to the Centers for Disease Control and Prevention (CDC).

There's no cure for either Crohn's or ulcerative colitis and no one surefire treatment for either. Instead, your doctor will likely ask you to try different diets and medications to find the right mix for you. In extreme cases, surgery may be necessary if you and your doctor are unable to control the inflammation.

Endocrine Disorders

Endocrine disorders—which are sometimes more commonly known as hormone imbalances—are another common cause of diarrhea.

Diabetes is a big one: "[Up to] 25% of people with long-standing diabetes have chronic diarrhea, particularly if they don't take good care of [their diabetes]," says Dr. Schiller. Some diabetes medications can lead to diarrhea, as can bacterial overgrowth related to diabetes, Dr. Ganjhu says.

An overactive thyroid (hyperthyroidism) is another common cause of diarrhea. "The thyroid gland sitting in the front of your neck helps control metabolism," explains Dr. Drake. "[An overactive thyroid] can cause weight loss, tremors, and heart palpitations. It also stimulates the gastrointestinal tract to move too quickly."

Addison's disease (when your body doesn't produce enough cortisol and other hormones from your adrenal gland) can also cause chronic diarrhea, per the NIDDK.

The good news, says Dr. Drake, is that there are treatments for all of these conditions, and they should relieve not just the diarrhea, but other symptoms as well.


Ironically enough, some of the medications used to treat bacterial diarrhea—namely, antibiotics—can actually also cause diarrhea. The problem is that antibiotics don't always distinguish between "bad" bacteria (which may be causing an infection) and "good" bacteria (which are vital to gut health), according to the Mayo Clinic. By changing your gut flora, antibiotics can also set the stage for infection with the Clostridium difficile bacterium, which can cause more chronic diarrhea.

Other medications can cause diarrhea, which can lead to chronic diarrhea if you take them for a long time, says Dr. De Latour. "Even your run-of-the-mill ibuprofen, Motrin, and Aleve can cause diarrhea, but people don't usually know that because they don't read the fine print, they just pop one in," she says.

Certain blood pressure medications, cancer drugs, antacids that contain magnesium (and anything that contains magnesium, which is used to treat constipation), and nonsteroidal anti-inflammatory drugs (NSAIDs) can also cause GI problems, including diarrhea.

Laxative Abuse

Although it might seem quite obvious, it's important to note that abusing laxatives can also cause chronic diarrhea. Laxative abuse is considered an eating disorder by the National Eating Disorders Association. Typically, someone misuses laxatives when they want to shed unwanted calories and lose weight—and thus, diarrhea is expected. But sometimes, Dr. Ganjhu says she sees patients who are using laxatives but still come to the doctor's offices complaining of frequent diarrhea. Luckily, laxative abuse doesn't cause lasting damage—once you stop using laxatives, the diarrhea should stop.

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