Diarrhea happens when your intestines push food through too quickly for water to be absorbed, or when something draws extra water into your bowel. The cause depends largely on how long it’s been going on: episodes lasting less than two weeks are usually triggered by infections or something you ate, while diarrhea persisting beyond four weeks points to a chronic condition, food intolerance, or medication side effect. Here’s how to narrow down what’s behind yours.
How Long It’s Lasted Matters
Gastroenterologists split diarrhea into three categories based on duration. Acute diarrhea lasts less than two weeks and is by far the most common. Persistent diarrhea runs two to four weeks. Chronic diarrhea lasts more than four weeks and almost always needs investigation.
If yours started in the last few days, the most likely culprits are a stomach bug, food poisoning, or a dietary trigger. If it’s been weeks or keeps coming back in waves, you’re looking at a different set of possibilities, from food intolerances to inflammatory conditions.
Infections: The Most Common Short-Term Cause
Viral gastroenteritis (the “stomach flu”) is the single most frequent reason for a sudden bout of diarrhea. Norovirus and rotavirus spread easily through contaminated surfaces and food, and symptoms typically resolve within a few days without treatment.
Bacterial food poisoning from organisms like Salmonella, Campylobacter, or E. coli tends to hit harder, often with cramping, nausea, and sometimes fever. Symptoms usually start 6 to 72 hours after eating contaminated food. Parasitic infections are less common but longer lasting. Giardia, for example, has an incubation period of one to two weeks after exposure and can cause watery diarrhea, bloating, and gas that drags on for two to six weeks.
Travel is a major risk factor. Unfamiliar water sources and different food-handling practices expose you to pathogens your body hasn’t encountered before.
Food and Drink Triggers
If your diarrhea seems tied to meals but you don’t feel sick otherwise, a food intolerance is a strong possibility. Unlike a food allergy, which involves the immune system, an intolerance means your gut can’t properly break down a specific compound.
Lactose intolerance is the most widespread example. People who don’t produce enough of the enzyme that breaks down milk sugar get bloating, gas, and diarrhea after consuming dairy. Fructose, found naturally in fruit and added to many processed foods as high-fructose corn syrup, causes similar problems in some people.
Sugar alcohols are a surprisingly common culprit that many people overlook. Ingredients like sorbitol, xylitol, and mannitol, found in sugar-free gum, protein bars, and diet candies, pull water into your intestines and can cause diarrhea even in small amounts. If you’ve recently started eating more “sugar-free” or “keto” products, that could be your answer.
Gluten, the protein in wheat, rye, and barley, triggers diarrhea in people with celiac disease and in some people with non-celiac gluten sensitivity. Histamine-rich foods like aged cheese, avocados, chocolate, and red wine can also cause digestive upset in people who don’t break down histamine efficiently.
Medications That Cause Diarrhea
Drug-induced diarrhea is extremely common and often goes unrecognized. If your symptoms started around the same time as a new prescription or supplement, that connection is worth exploring.
Antibiotics are the most well-known offenders. They disrupt the balance of bacteria in your gut, and diarrhea can start during a course of antibiotics or even a week or two after finishing one. Metformin, widely prescribed for type 2 diabetes, causes diarrhea in a significant number of people, especially when first starting the medication or after a dose increase.
Other common triggers include magnesium-containing antacids, heartburn medications like omeprazole and famotidine, NSAIDs like ibuprofen and naproxen, and chemotherapy drugs. Even over-the-counter supplements with high doses of magnesium or vitamin C can loosen stools.
Chronic Conditions to Consider
When diarrhea keeps coming back or never fully goes away, three conditions come up most often: irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and celiac disease. They can look similar on the surface but are fundamentally different.
IBS is a functional disorder, meaning your gut doesn’t work quite right but isn’t physically damaged. It doesn’t cause inflammation, doesn’t affect other parts of your body, and isn’t autoimmune. The diarrhea-predominant form (IBS-D) typically involves cramping, urgency, and loose stools that worsen with stress or certain foods. It’s diagnosed after other conditions have been ruled out.
IBD, which includes Crohn’s disease and ulcerative colitis, is an autoimmune condition that causes real physical damage to the digestive tract. It often produces symptoms beyond the gut, including joint pain, skin problems, and fatigue. Bloody stool, weight loss, and persistent pain are more characteristic of IBD than IBS.
Celiac disease is triggered specifically by gluten and damages the lining of the small intestine. Unlike IBD, which can affect any part of the digestive system, celiac disease is confined to the small intestine and fully resolves on a strict gluten-free diet. A blood test can screen for it, followed by a biopsy to confirm.
What’s Happening Inside Your Gut
Not all diarrhea works the same way at a biological level, and understanding the difference can help you identify the cause. There are two main patterns.
In one type, unabsorbed substances in your intestine hold onto water like a sponge. This is what happens with lactose intolerance, sugar alcohols, and certain laxatives. A key clue: this type of diarrhea improves when you stop eating and gets worse after meals. If fasting makes your symptoms better, something in your diet is likely responsible.
In the other type, your intestinal lining actively secretes extra fluid. This happens with certain infections, bile acid problems, microscopic colitis, and some medications. The telltale sign is that diarrhea continues even when you haven’t eaten, and it often persists at night, waking you from sleep. Nighttime diarrhea in particular suggests something beyond a simple dietary trigger.
What to Eat During a Flare
The old advice to stick strictly to bananas, rice, applesauce, and toast (the BRAT diet) is outdated. There are no studies showing it works better than simply eating bland, easy-to-digest foods. It’s fine for a day or two, but it lacks the protein and nutrients your body needs to recover.
Better options include brothy soups, oatmeal, boiled potatoes, crackers, and unsweetened dry cereals. Once your stomach settles, add cooked carrots, sweet potatoes without skin, cooked squash, avocado, skinless poultry, fish, and eggs. These are all gentle on the gut while providing real nutrition.
Staying hydrated matters more than food choices. Diarrhea pulls water and electrolytes out of your body quickly. Sip water, diluted juice, or an oral rehydration solution throughout the day rather than drinking large amounts at once.
Signs That Need Medical Attention
Most acute diarrhea resolves on its own. But certain symptoms signal something more serious. Bloody or black stools, a fever above 102°F (39°C), severe abdominal or rectal pain, and signs of dehydration like excessive thirst, very dark urine, dizziness, or dry mouth all warrant prompt medical evaluation.
For adults, diarrhea that lasts more than two days without any improvement is worth a call to your doctor. Children, older adults, and people with weakened immune systems are more vulnerable to dehydration. In a young child, watch for no wet diaper in three or more hours, crying without tears, or unusual sleepiness.
If your diarrhea is chronic and you haven’t been evaluated, keeping a food and symptom diary for two weeks before your appointment can be genuinely useful. Track what you eat, when symptoms hit, and how severe they are. Patterns often emerge that point toward a food intolerance, a medication effect, or a condition worth testing for.