Diarrhea: Causes, Home Care, and When to Worry

Most diarrhea is acute, viral, and resolves on its own in under a week. The only thing it really needs is fluid and electrolytes (NIDDK). What separates a normal stomach bug from something that needs a clinician is duration and company: diarrhea lasting more than two days in adults, or paired with high fever, blood in the stool, severe pain, or signs of dehydration, is the part you don’t ride out at home (Mayo Clinic). A few common moves can actually make things worse: reaching for loperamide when you have a fever and bloody stool, or asking for antibiotics for any food-poisoning episode.

Key takeaways

• Diarrhea is medically defined as three or more loose, watery stools in a day, or noticeably more frequent or watery than your normal (NIDDK).
• Acute lasts under 2 weeks, persistent runs 2–4 weeks, and chronic is 4 weeks or more. The categories matter because the causes (and workup) differ.
• Most acute cases are viral and self-limited. Oral rehydration solution (ORS) is the first-line treatment; sports drinks have too little sodium to fully replace losses (AAFP).
• Loperamide is not for everyone. Avoid it with bloody stools, high fever, or in children with acute diarrhea (IDSA 2017). Antibiotics can be harmful in Shiga-toxin E. coli infections; they raise the risk of hemolytic uremic syndrome.
• Red flags include blood, black/tarry stools, fever above 102 °F (39 °C), severe abdominal pain, signs of dehydration, or symptoms longer than 48 hours in adults. Stop self-treating and call a clinician.

What counts as diarrhea

The clinical definition is simple: three or more loose or watery stools in 24 hours, or stool that’s noticeably more frequent or looser than your normal baseline (NIDDK). On the Bristol Stool Scale, that maps to Type 6 (mushy, ragged edges, mild diarrhea) and Type 7 (entirely liquid, frank diarrhea).

Duration is the single most useful split:

• Acute diarrhea: under 2 weeks. Almost always infectious or food-related. Self-limited in healthy adults.
• Persistent diarrhea: 2 to 4 weeks. Usually still infectious (parasites become more likely), but the door opens to medication effects and post-infectious IBS.
• Chronic diarrhea: 4 weeks or more. Now you’re looking at IBS-D, IBD (Crohn’s, ulcerative colitis), microscopic colitis, celiac disease, lactose or other carbohydrate intolerances, bile-acid malabsorption, and pancreatic insufficiency.

What causes acute diarrhea

The everyday causes line up in a short list.

Viral gastroenteritis

Norovirus and rotavirus are the two big offenders, with norovirus dominant in adults. Onset is usually 12–48 hours after exposure, symptoms peak fast, and the whole thing is over in 1–3 days. Vomiting plus diarrhea points strongly to a virus.

Bacterial infections (food poisoning)

Salmonella, Campylobacter, Shigella, Shiga-toxin–producing E. coli (STEC), and Vibrio species cause most US foodborne diarrhea. Bacterial diarrhea tends to be more severe, more likely to be bloody, and more likely to come with high fever. Those are the features that flip the algorithm from “ride it out” to “see a clinician.”

Traveler’s diarrhea

If you crossed a border in the last two weeks, suspicion shifts. Attack rates run 30%–70% within the first two weeks of travel to high-risk regions, and bacterial pathogens (most commonly enterotoxigenic E. coli) account for over 80% of cases (CDC EID, 2024).

Parasites

Giardia, Cryptosporidium, and Entamoeba histolytica show up in well/stream water, daycare outbreaks, and travel exposure. Parasitic diarrhea is the most common reason an episode drags past two weeks.

Medications

Antibiotics are the heaviest hitter. They wipe out commensal flora and let Clostridioides difficile (C. diff) overgrow, especially in people who were recently hospitalized or older than 65. Other common culprits: metformin, magnesium-containing antacids, proton-pump inhibitors, NSAIDs, SSRIs, and chemotherapy agents.

Food intolerances and additives

Lactose intolerance, sugar alcohols (sorbitol, mannitol, xylitol, the “sugar-free gum” diarrhea), excess fructose, and high-FODMAP foods can all trigger osmotic diarrhea within a few hours of a meal.

What causes chronic diarrhea

When stools have been loose for four weeks or longer, the differential broadens and self-treatment isn’t enough. The big categories:

• IBS-D (irritable bowel syndrome with diarrhea): diagnosed by symptom criteria after ruling out organic disease. Often improves on a low-FODMAP diet. See our IBS deep dive for the full picture.
• Inflammatory bowel disease (Crohn’s, ulcerative colitis): bloody diarrhea, weight loss, nighttime symptoms, and elevated inflammatory markers point this direction.
• Celiac disease: a meaningful share of chronic-diarrhea workups end with a celiac diagnosis; gluten withdrawal resolves the symptoms.
• Microscopic colitis: watery, non-bloody diarrhea, often in older women and sometimes triggered by NSAIDs or PPIs. Diagnosis requires colonoscopy with biopsy.
• Bile-acid diarrhea: under-recognized. Bile acids that should be reabsorbed in the terminal ileum reach the colon and trigger secretion. Often misdiagnosed as IBS-D.
• Pancreatic exocrine insufficiency: fatty, oily, hard-to-flush stools. Pairs with weight loss.

If diarrhea has lasted four weeks or more, that’s the cue for a clinical workup, not another round of Imodium.

How to treat diarrhea at home

For uncomplicated acute diarrhea in a healthy adult, the playbook is short.

1. Replace fluid and electrolytes properly

Loose stools dump water, sodium, potassium, and bicarbonate. The evidence-based first move is oral rehydration solution (ORS), not water alone and not most sports drinks. The WHO reduced-osmolarity formula has roughly 75 mEq/L sodium and 75 mEq/L glucose (AAFP). A typical sports drink is closer to 18 mEq/L sodium, which is inadequate when you’re actively losing fluid.

Practical options:

• Pre-mixed ORS packets (Pedialyte, Hydralyte, DripDrop, Liquid I.V. ORS).
• Homemade ORS: 1 liter of water + 6 level teaspoons sugar + ½ level teaspoon salt (the WHO recipe).
• For mild cases, broths and salty foods plus water work fine. Most people don’t need formal ORS for a 24-hour bug.

Pale-yellow urine across the day is the rough hydration target.

2. Eat normally; skip the BRAT diet

The old advice (bananas, rice, applesauce, toast) has been retired by the American Academy of Pediatrics and most major societies. The BRAT diet is too restrictive, supplies roughly 300 fewer calories per day than a normal toddler diet, and lacks fat, protein, and several micronutrients (Cleveland Clinic). Current guidance is to resume a regular age-appropriate diet as soon as it’s tolerated. Early refeeding shortens illness, reduces stool output, and improves nutrition.

Practical version for adults: eat what sounds tolerable. Soup, eggs, plain pasta, yogurt, fruit, lean protein. Avoid only what obviously makes things worse for you (often greasy food, alcohol, large amounts of caffeine, and high-FODMAP items during recovery).

3. Use loperamide carefully, and know when not to

Loperamide (Imodium) slows gut motility. The OTC dose is 4 mg up front, then 2 mg after each unformed stool, max 8 mg/day (StatPearls). It’s reasonable for uncomplicated, watery, non-bloody diarrhea in immunocompetent adults, for example when you need to get through a flight.

When to skip loperamide entirely, per the IDSA 2017 guideline:

• Bloody diarrhea or visible mucus. See mucus in stool and black stool causes for the differential.
• High fever (above ~101.3 °F / 38.5 °C) suggesting invasive bacterial infection.
• Suspected C. diff, especially after recent antibiotics or hospitalization.
• Children with acute diarrhea. Antimotility drugs are not recommended in pediatric infectious diarrhea.

Bismuth subsalicylate (Pepto-Bismol) is a milder alternative for adults, with antimicrobial and anti-secretory effects. It also turns the stool and tongue black temporarily, which is harmless but easy to mistake for a GI bleed.

4. Antibiotics: when they help, when they hurt

Most acute infectious diarrhea is viral, and antibiotics do nothing. Even most bacterial cases self-resolve. Where antibiotics do help:

• Severe traveler’s diarrhea: targeted regimens shorten symptoms.
• Confirmed Shigella, Campylobacter, Vibrio cholerae, Giardia, or amebiasis: treated by symptom severity and pathogen.
• C. diff: specific therapy (vancomycin or fidaxomicin), not just any antibiotic.

Where antibiotics actively harm: Shiga-toxin-producing E. coli (STEC O157 and others). The IDSA gave a strong recommendation against antibiotics in confirmed or suspected STEC because they raise the risk of hemolytic uremic syndrome (HUS), with kidney injury, low platelets, and hemolytic anemia (IDSA 2017). This is why “I have bloody diarrhea, give me antibiotics” is the wrong reflex without testing.

Red flags: when to stop self-treating

From the Mayo Clinic and IDSA 2017, the features that turn diarrhea into a clinic visit:

• Diarrhea lasting more than 2 days in adults (24 hours in children, sooner in infants).
• Blood in the stool, black tarry stools, or significant rectal bleeding.
• Fever above 102 °F (39 °C).
• Severe abdominal or rectal pain.
• Signs of dehydration: lightheadedness, very dark urine, dry mouth, low urine output, weakness.
• Recent antibiotics or hospitalization (raises C. diff suspicion).
• Travel to a high-risk region in the last few weeks.
• Pregnancy, age >65, immunocompromise, or chronic illness (lower threshold for evaluation).
• Diarrhea lasting 4 weeks or more: chronic diarrhea workup, not another OTC.

FAQ

How long is “normal” for a stomach bug? For viral gastroenteritis in healthy adults, 1–3 days is typical, and it’s almost always resolved by day 7. If diarrhea is still going at 14 days, that’s persistent diarrhea and worth a clinical evaluation — parasites and post-infectious IBS become more likely.

Should I take Imodium or just ride it out? For uncomplicated, watery, non-bloody diarrhea in a healthy adult, loperamide is reasonable when you need symptom control. Skip it if you have bloody stools, high fever, signs of sepsis, recent antibiotics (C. diff risk), or you’re treating a child — in those cases, slowing the gut can trap pathogens and worsen the illness.

Are sports drinks good enough for rehydration? Not really. Sports drinks have roughly a quarter the sodium of WHO oral rehydration solution and a lot more sugar. They’re fine for mild dehydration in a healthy adult who is also eating salty food, but for moderate dehydration, kids, or anyone over 65, use a proper ORS like Pedialyte or DripDrop (AAFP).

When does diarrhea need antibiotics? Rarely. Most acute diarrhea is viral or self-limited bacterial. Antibiotics help in severe traveler’s diarrhea, confirmed Shigella or Vibrio, parasitic infections like Giardia, and C. diff — and they’re contraindicated in Shiga-toxin E. coli because they raise HUS risk (IDSA 2017). Stool testing usually comes before antibiotics, not after.

Is the BRAT diet still recommended? No. The American Academy of Pediatrics and Cleveland Clinic both moved away from BRAT — it’s nutritionally too thin and there’s no evidence it shortens illness. The current advice is to eat a normal, age-appropriate diet as soon as it’s tolerated (Cleveland Clinic).

My diarrhea has been off and on for two months — is that IBS? Maybe, but IBS is a diagnosis of exclusion. Diarrhea lasting four weeks or more deserves a workup before settling on IBS-D — labs to rule out celiac and inflammation, sometimes stool studies, sometimes colonoscopy. See our IBS overview for what that workup looks like, and our low-FODMAP guide for one of the most evidence-backed dietary approaches once IBS-D is confirmed.

The bottom line

Most diarrhea is short, viral, and forgiving — fluids and electrolytes are doing 90% of the work. The mistakes worth avoiding are reaching for loperamide with bloody or febrile diarrhea, asking for antibiotics for food poisoning that doesn’t need them, restricting eating with the BRAT diet when normal food is better, and waiting too long with red-flag symptoms. If diarrhea passes the 48-hour mark in an adult, brings blood, fever, or severe pain, or has been off and on for four weeks or more, that’s the line where home care stops and a clinician starts.

PoopCheck logs Bristol type, stool color, and frequency from a photo, so you can tell exactly when an episode started, how long it’s actually lasted, and whether the trend is moving back toward Type 4 or stuck at Type 6–7. That’s the data your clinician will ask for if a workup is warranted — and the data most people otherwise can’t reconstruct from memory. See our constipation companion piece for the other side of the Bristol scale.

Sources

1. Definition & Facts for Diarrhea — National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), NIH.
2. Diarrhea — When to see a doctor — Mayo Clinic.
3. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea — Shane AL et al., Clin Infect Dis 2017;65(12):e45–e80.
4. Etiology and Epidemiology of Travelers’ Diarrhea among US Military and Adult Travelers, 2018–2023 — Emerging Infectious Diseases, CDC, 2024.
5. Oral Rehydration Solutions for the Treatment of Acute Watery Diarrhea — American Family Physician, 2017.
6. What Is the BRAT Diet, and Should You Try It? — Cleveland Clinic.
7. Loperamide — StatPearls — National Library of Medicine, NIH.