Diarrhea is loose, watery stool that occurs more frequently than normal, typically three or more times a day. It’s one of the most common health complaints worldwide, causing an estimated 1.17 million deaths globally in 2021, mostly in young children in low-resource settings. For most adults in developed countries, a bout of diarrhea is uncomfortable but short-lived, resolving on its own within a few days.
What Happens in Your Gut
Your intestines normally absorb water from the food and liquid you consume, leaving behind a soft but formed stool. Diarrhea occurs when that process breaks down. There are a few ways this can happen.
Sometimes your gut can’t absorb certain substances properly, and those substances pull extra water into the intestines by osmotic force. This is what happens with lactose intolerance or after eating sugar-free candies sweetened with sugar alcohols. Other times, an infection or toxin triggers your intestinal lining to actively pump fluid into the gut, reversing its normal absorption. Bacterial toxins from food poisoning often work this way. Inflammation from conditions like Crohn’s disease or ulcerative colitis can damage the intestinal wall itself, causing fluid, blood, and mucus to leak into the stool. And in some cases, food simply moves through the intestines too quickly for water to be absorbed, which is common with irritable bowel syndrome (IBS) and overactive thyroid.
Common Causes
Most acute diarrhea (the kind that comes on suddenly and lasts a few days) is caused by infections. Viruses are the most frequent culprit: norovirus in adults and rotavirus in young children. COVID-19 can also cause gastrointestinal symptoms including diarrhea. Bacteria like E. coli and Salmonella typically come from contaminated food or water. C. diff is a bacterium that commonly causes diarrhea after a course of antibiotics or during a hospital stay, because antibiotics wipe out the normal gut bacteria that keep it in check.
Dietary triggers are another common cause. Coffee, dairy products, artificial sweeteners, and high-fat foods can all loosen stools in susceptible people. Medications are a frequently overlooked source, particularly antibiotics, antacids containing magnesium, and certain cancer drugs.
When diarrhea persists beyond a few days, it often points to a different set of causes: IBS, celiac disease, inflammatory bowel disease (Crohn’s or ulcerative colitis), small intestinal bacterial overgrowth (SIBO), or microscopic colitis. Chronic diarrhea deserves a conversation with your doctor because the underlying condition typically needs its own treatment.
Dehydration Is the Real Risk
Diarrhea itself is usually not dangerous. The danger comes from losing too much fluid and electrolytes. This is especially true for infants, young children, older adults, and people with weakened immune systems.
In adults, early signs of dehydration include dark-colored urine, urinating less often, dry mouth, and fatigue. You can check skin turgor by gently pinching the skin on the back of your hand. If it doesn’t flatten back right away, you may be dehydrated. In infants and young children, watch for no wet diapers for three hours, a dry mouth, crying without tears, and skin that stays tented after a gentle pinch.
Replacing lost fluids is the single most important thing you can do. Water alone isn’t ideal because it lacks the electrolytes your body is losing. A simple oral rehydration solution based on the WHO recipe calls for half a teaspoon of salt and two tablespoons of sugar dissolved in about one liter of water. This combination works because the sugar helps your intestines absorb the sodium, which in turn pulls water back into your body. Store-bought options like Pedialyte follow the same principle. For a more palatable version, you can mix one cup of orange juice with four cups of water, two and a half tablespoons of sugar, three-quarters of a teaspoon of baking soda, and half a teaspoon of salt.
What to Eat During a Bout
You may have heard of the BRAT diet (bananas, rice, applesauce, toast) as the go-to recommendation for diarrhea. Major health organizations, including the American Academy of Pediatrics, the CDC, and the WHO, no longer recommend it. Research has shown that restricting your diet to just a few bland foods can impair nutritional recovery and, in children, potentially lead to malnutrition.
The current guidance is straightforward: once you’re rehydrated, resume eating a normal, varied diet as soon as you can tolerate it. Breastfed infants should continue nursing. Formula-fed infants should stay on their regular full-strength formula. Older children and adults should eat age-appropriate foods from a variety of sources. You don’t need to starve a stomach bug. Your gut actually recovers faster when it has nutrients to work with. That said, it’s reasonable to temporarily avoid greasy foods, caffeine, and dairy if they seem to worsen your symptoms.
Over-the-Counter Treatments
Loperamide (sold as Imodium) works by slowing down intestinal movement, giving your gut more time to absorb water. The typical adult dose is two tablets or capsules after the first loose stool, then one after each subsequent loose stool, up to a maximum of four tablets in 24 hours for the over-the-counter version. It can provide real relief for travel diarrhea or inconvenient timing, but it should not be used if you have a high fever, bloody stools, or diarrhea caused by a bacterial infection like C. diff. In those situations, slowing the gut down can actually make things worse by keeping the bacteria or toxins inside longer.
Bismuth subsalicylate (Pepto-Bismol) is another option that can reduce the number of loose stools and ease cramping. It works differently, coating the intestinal lining and having a mild antimicrobial effect. It will turn your stool and tongue black temporarily, which is harmless but can be alarming if you’re not expecting it.
Warning Signs That Need Attention
Most diarrhea resolves on its own. But certain symptoms signal something more serious. Contact a doctor promptly if you experience any of the following: diarrhea lasting more than two days in adults (or more than one day in children), a high fever, six or more loose stools per day, severe abdominal or rectal pain, stools that are black and tarry or contain blood or pus, or signs of dehydration like very dark urine and dizziness.
In infants and children, the timeline is shorter. Seek help if a child refuses to eat or drink for more than a few hours, has any fever (in infants under 12 months), or shows signs of dehydration. Pregnant women, adults over 65, people currently on antibiotics, and anyone with a weakened immune system should have a lower threshold for reaching out to their doctor.
How Doctors Investigate Persistent Diarrhea
If diarrhea doesn’t resolve or keeps coming back, your doctor may order stool tests to look for bacteria, viruses, or parasites. A parasite screen is more likely if you’ve traveled internationally, drunk untreated water from a lake or stream, or have symptoms like unusually foul-smelling, greasy stools that float, along with weight loss. Sometimes the first test comes back negative, and a second sample or a different type of test is needed.
For chronic diarrhea, testing often broadens to include blood work for celiac disease, imaging of the intestines, or a colonoscopy to look for inflammatory bowel disease. Breath tests can help identify lactose intolerance or bacterial overgrowth. The specific testing path depends on your symptoms, how long they’ve lasted, and what patterns your doctor notices.