Most diarrhea is caused by something temporary: a virus, something you ate, or a medication you recently started. It resolves on its own within a few days. But when loose stools keep coming back or last longer than expected, the cause usually falls into a handful of well-understood categories, and identifying which one applies to you is the fastest path to fixing it.
How Your Gut Produces Diarrhea
Your intestines constantly balance two processes: absorbing fluid from what you eat and drink, and secreting fluid to help move things along. Diarrhea happens when that balance tips toward too much fluid staying in the bowel. This can happen in two main ways.
The first is when something in your gut pulls water in. Certain foods, sweeteners, or poorly absorbed sugars create an osmotic effect, drawing extra fluid into your intestines. This is why eating too much candy or drinking a sugar-heavy drink can send you to the bathroom. The key feature: this type stops when you stop eating the trigger.
The second is when the lining of your intestine actively pumps fluid outward, often because a toxin or infection has hijacked the normal signaling. Bacterial toxins from food poisoning, for example, can flip that secretory switch. This type continues even if you stop eating entirely, which is why stomach bugs can keep you miserable for days regardless of what you do.
Viral and Bacterial Infections
Viral infections are the single most common cause of acute diarrhea. Norovirus and rotavirus spread easily through contaminated surfaces, food, or close contact with someone who’s sick. These infections typically hit fast, bring nausea and cramping along with watery stools, and clear up within one to three days.
When bacteria are the culprit, the most frequently identified causes in the United States are Salmonella, Campylobacter, Shigella, and a toxin-producing strain of E. coli. Bacterial diarrhea tends to be more severe than viral, sometimes producing fever, bloody stools, or symptoms that last longer than a week. Undercooked poultry, contaminated produce, and improperly stored food are the usual sources.
Foods and Sweeteners That Trigger Loose Stools
Your diet is one of the most overlooked causes of recurring diarrhea. Sugars stimulate your gut to release water and electrolytes, loosening bowel movements. If you consume a lot of sugar in one sitting, diarrhea can follow even without any infection or underlying condition.
Artificial sweeteners are especially potent triggers. Sorbitol, mannitol, and xylitol, found in sugar-free gum, candy, and some medications, are poorly absorbed and draw water into the intestine. Fructose and lactose do the same thing in people who don’t digest them well. All of these belong to a group called FODMAPs: short-chain carbohydrates that ferment in the gut and cause bloating, gas, and diarrhea in sensitive individuals.
Common high-FODMAP foods include wheat, rye, onions, garlic, legumes (chickpeas, lentils, beans), honey, pistachios, cashews, asparagus, and artichokes. If you notice diarrhea flaring after meals but can’t pin down a pattern, keeping a food diary for two weeks and cross-referencing it with this list can be revealing. Many people discover a single food group is responsible for most of their symptoms.
Medications You Might Not Suspect
Several widely used medications cause diarrhea as a side effect. Antibiotics are the most well-known offenders. Your intestines host a complex community of bacteria that normally keep each other in check. Antibiotics kill some of those bacteria, allowing others to overgrow. In some cases, this creates an opening for a bacterium called C. difficile, which can cause severe, watery, and sometimes bloody diarrhea.
Magnesium-containing antacids are another common cause, since magnesium draws water into the bowel. Metformin, one of the most prescribed diabetes medications, frequently causes diarrhea, particularly in the first few weeks of use. If your diarrhea started shortly after beginning a new medication, that timing is worth noting.
For antibiotic-related diarrhea specifically, certain probiotics have solid evidence behind them. Preparations containing Lactobacillus rhamnosus GG or Saccharomyces boulardii (a strain of brewer’s yeast) at doses of 5 to 40 billion colony-forming units per day have shown the most consistent results in preventing antibiotic-associated diarrhea.
Acute, Persistent, and Chronic Diarrhea
Doctors categorize diarrhea by how long it lasts, and those categories matter because they point to different causes. Acute diarrhea lasts less than two weeks and is almost always from an infection or something you ate. Persistent diarrhea lasts two to four weeks and may signal an infection that hasn’t fully cleared or an ongoing dietary trigger. Chronic diarrhea, lasting more than four weeks, suggests something more structural is going on.
Chronic diarrhea has a longer list of possible causes. Irritable bowel syndrome with diarrhea (IBS-D) is one of the most common, producing recurrent loose stools tied to abdominal pain that improves after a bowel movement. Inflammatory bowel diseases like Crohn’s and ulcerative colitis cause chronic diarrhea through ongoing inflammation in the intestinal lining. Celiac disease, an autoimmune reaction to gluten, and chronic infections can also be responsible. Thyroid disorders, particularly an overactive thyroid, sometimes cause persistent loose stools that people don’t connect to the underlying condition.
If your diarrhea has lasted more than four weeks, identifying a specific cause rather than just managing symptoms becomes important, because many of these conditions respond well to targeted treatment.
Dehydration and Warning Signs
The biggest immediate risk from diarrhea isn’t the diarrhea itself. It’s fluid loss. Your body can lose significant amounts of water and electrolytes through frequent loose stools, especially if vomiting is happening at the same time. Drinking water helps, but replacing electrolytes (sodium, potassium) matters too. Oral rehydration solutions or broths are more effective than plain water alone.
Certain symptoms signal that something more serious is happening and shouldn’t be managed at home:
- Duration: diarrhea lasting more than two days without any improvement
- Blood: bloody or black stools
- Fever: temperature above 102°F (39°C)
- Dehydration signs: excessive thirst, dry mouth, very dark urine, little or no urination, dizziness, or severe weakness
- Pain: severe abdominal or rectal pain
For children, the timeline is shorter. Diarrhea that doesn’t improve within 24 hours, no wet diaper in three or more hours, or signs like a dry mouth, no tears when crying, or unusual sleepiness all warrant prompt medical attention. Children dehydrate faster than adults, and their symptoms can escalate quickly.
Simple Steps That Help Most Cases
For garden-variety acute diarrhea, the most effective approach is straightforward. Stay hydrated with fluids that contain some salt and sugar. Eat bland, easy-to-digest foods when you feel ready: rice, bananas, toast, plain chicken. Avoid dairy, caffeine, alcohol, and high-fat or high-fiber foods until things settle down, since these can all worsen symptoms.
Over-the-counter anti-diarrheal medications can reduce the frequency of stools and are generally fine for mild viral or dietary diarrhea. However, if you have a high fever or bloody stools, these medications can actually make things worse by trapping a bacterial infection inside the gut longer.
If your diarrhea keeps returning, the most productive next step is looking for a pattern. Track what you eat, what medications you take, and when symptoms appear. Many people with chronic or recurring diarrhea find a dietary trigger, a medication side effect, or a treatable condition like celiac disease or IBS once they start paying close attention to timing.