Diarrhea has dozens of possible causes, ranging from something you ate last night to a chronic condition that needs long-term management. Most cases are acute, lasting less than two weeks, and resolve on their own. But when loose stools persist for more than four weeks, something deeper is usually going on. Here’s a breakdown of the most common triggers.
Infections: The Most Common Acute Cause
Viruses are the leading cause of short-term diarrhea. Norovirus is the biggest culprit in adults (and the reason entire cruise ships get sick), while rotavirus historically hits young children hardest. Adenovirus and astrovirus are less well known but still widespread. These infections typically cause watery diarrhea, nausea, and sometimes vomiting that clears within a few days.
Bacterial infections tend to hit harder. Salmonella, Campylobacter, Shigella, and certain strains of E. coli can all cause diarrhea that’s more severe, sometimes bloody, and often accompanied by fever and cramping. You pick these up from contaminated food, undercooked meat, unpasteurized dairy, or contaminated water. Parasites like Giardia and Cryptosporidium are less common in developed countries but are a major cause of prolonged diarrhea after travel or exposure to untreated water.
Foods and Drinks That Trigger Loose Stools
Lactose intolerance is the most common food-related cause. If your body doesn’t produce enough of the enzyme that breaks down the sugar in milk, that undigested lactose travels to your colon, where bacteria ferment it. The fermentation produces gas, and the unabsorbed sugar draws water into the intestine, leading to bloating, cramping, and diarrhea. Fructose malabsorption works the same way and is surprisingly common. High-fructose corn syrup, honey, apples, and pears are frequent offenders.
Gluten causes diarrhea in people with celiac disease or gluten sensitivity. In celiac disease, gluten triggers an immune response that damages the lining of the small intestine, impairing its ability to absorb nutrients across the board.
Caffeine speeds up contractions in the colon. A cup or two of coffee may cause no problems, but higher amounts can push things through too fast. Alcohol, especially in large quantities, irritates the gut lining and disrupts absorption. Spicy foods can also accelerate motility in sensitive individuals.
Sugar-Free Products and Sugar Alcohols
If you’ve ever eaten a handful of sugar-free gummy bears and regretted it, you’ve experienced polyol-induced diarrhea. Sugar alcohols like sorbitol, mannitol, xylitol, and erythritol are used in sugar-free gum, candy, protein bars, and diet drinks. Your small intestine absorbs them poorly, so they pass into the colon and pull water in behind them, creating a laxative effect.
The effect is dose-dependent: a stick of sugar-free gum is unlikely to cause problems, but a bag of sugar-free candy easily can. Malabsorption gets worse when you consume multiple types of sugar alcohols together, which is common in processed “low-carb” or “keto” products. People with IBS are especially sensitive.
Medications That Cause Diarrhea
Antibiotics are one of the most common medication-related causes. They work by killing bacteria, but they don’t distinguish between harmful bacteria and the beneficial ones in your gut. When that balance gets disrupted, opportunistic bacteria can overgrow. In serious cases, a bacterium called C. difficile takes over, causing severe, watery, and sometimes bloody diarrhea that requires its own course of treatment.
Magnesium-containing antacids draw water into the intestine and can cause or worsen diarrhea, especially at higher doses. Chemotherapy drugs frequently cause diarrhea because they damage fast-dividing cells throughout the body, including those lining the gut. Certain blood pressure medications, diabetes drugs, and anti-inflammatory painkillers can also be responsible. If diarrhea starts within days of beginning a new medication, that timing is worth noting.
Stress and the Gut-Brain Connection
Your brain and your digestive system are in constant communication through a network of nerves, hormones, and immune signals. Stress, anxiety, and depression don’t just affect your mood. They directly alter the movement and contractions of your GI tract. This is why you might get loose stools before a job interview, during a difficult week at work, or in the middle of a personal crisis. The effect is real and physiological, not “all in your head.” For people with IBS, stress is one of the most reliable triggers for flare-ups.
Irritable Bowel Syndrome
IBS is a chronic functional disorder, meaning it changes how the gut behaves without causing visible damage to the tissue. The diarrhea-predominant form (IBS-D) causes frequent loose stools, urgency, and abdominal pain that often improves after a bowel movement. Stool volumes tend to be relatively small (under 350 mL per day), and symptoms rarely wake you up at night, which helps distinguish IBS from more serious conditions. Triggers vary from person to person but commonly include certain foods, hormonal changes, and stress.
Inflammatory Bowel Disease
Crohn’s disease and ulcerative colitis are the two main forms of inflammatory bowel disease. Unlike IBS, these conditions involve actual inflammation and damage to the intestinal lining. Diarrhea from IBD can include blood, mucus, or pus, and often comes with fatigue, weight loss, and fever during flares. Both are lifelong conditions that require ongoing management. Because IBD and IBS share surface-level symptoms like stomach pain and changes in bowel habits, the two are frequently confused, but they are fundamentally different diseases.
Bile Acid Malabsorption
Your liver produces bile to help digest fats. Normally, most of that bile gets reabsorbed in the small intestine and recycled. When too much bile escapes into the colon, it triggers the colon to secrete water, producing chronic, watery diarrhea. This can happen on its own or as a result of other conditions affecting the small intestine.
Gallbladder removal is a particularly common cause. Research suggests roughly half of people who have their gallbladder removed experience diarrhea afterward, likely because bile flows continuously into the intestine rather than being stored and released in controlled amounts. For most people this resolves within weeks, but in rare cases it can persist for years.
How Long It Lasts Matters
The duration of your diarrhea is one of the most useful clues to its cause. Acute diarrhea, lasting less than two weeks, is most often caused by infections or something you ate. Persistent diarrhea lasts two to four weeks and sometimes signals an infection that hasn’t fully cleared or a medication side effect. Chronic diarrhea, lasting more than four weeks, points toward conditions like IBS, IBD, celiac disease, or malabsorption problems that benefit from medical evaluation.
Signs That Need Prompt Attention
Most diarrhea is uncomfortable but not dangerous. However, certain symptoms change the picture. Blood or black color in your stool, a fever above 102°F, severe abdominal pain, and signs of dehydration (excessive thirst, dark urine, dizziness, dry mouth, little or no urination) all warrant medical attention. For adults, diarrhea lasting more than two days without any improvement is also worth a call to your doctor. For children, the threshold is lower: diarrhea that doesn’t improve within 24 hours, no wet diaper in three or more hours, or signs like a dry mouth, sunken eyes, or unusual drowsiness should be evaluated quickly. Dehydration develops faster in young children and can become serious.