Diarrhea means passing loose or watery stools three or more times a day, or more often than is normal for you. Most episodes are acute: they come from a stomach virus, food poisoning or a medicine, last less than a week and go away on their own. The first job is not to stop the diarrhea at all costs. It is to replace the water and salts you are losing.
How long it lasts tells you a lot. Diarrhea that lasts 2 to 4 weeks is called persistent, and diarrhea lasting at least 4 weeks is chronic. Chronic diarrhea affects roughly 6% to 7% of US adults, and more than 90% of these cases are not caused by an infection. Irritable bowel syndrome, celiac disease, bile acid diarrhea, microscopic colitis and inflammatory bowel disease top the list.
Below: the causes, how to stop diarrhea safely, the warning signs, and the stool and blood tests that find the cause, with their numbers.
Key takeaways
- Most acute diarrhea is viral, mainly norovirus, and settles in 1 to 3 days.
- Oral rehydration solution comes first; loperamide or bismuth help most adults, but not with blood or fever.
- See a doctor after 2 days (1 day for a child), or with 6 or more stools a day, blood, high fever or dehydration.
- Persistent or chronic diarrhea deserves stool and blood tests: PCR panel, C. difficile, calprotectin, tTG-IgA, electrolytes.
- A fecal calprotectin of 40 µg/g or less makes inflammatory bowel disease very unlikely.
What is diarrhea?
The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) defines diarrhea as loose, watery stools three or more times a day, or more often than what is normal for you. On the Bristol stool chart, types 6 and 7 (mushy or entirely liquid) count as diarrhea; our guide to stool consistency and the Bristol scale shows each type.
Doctors sort diarrhea by duration:
- Acute diarrhea: usually less than a week, often 1 to 3 days. Americans have about one episode a year.
- Persistent diarrhea: longer than 2 weeks but less than 4 weeks. Parasites become more likely.
- Chronic diarrhea: at least 4 weeks. Infection becomes rare.
The type of stool also helps. Watery stools suggest a virus or toxin, bloody stools with fever (dysentery) an invasive bacterium, and greasy, floating stools poor fat absorption, as explained in our article on fatty stool.
What causes diarrhea?
Infections: the main cause of acute diarrhea
Norovirus is the leading cause of vomiting and diarrhea, and of foodborne illness, in the United States. The CDC estimates 19 to 21 million illnesses, 109,000 hospitalizations and about 900 deaths a year, mostly among adults 65 and older. Symptoms start 12 to 48 hours after exposure and usually last 1 to 3 days.
Bacteria cause most cases of bloody or "explosive" diarrhea with fever: Salmonella, Campylobacter, Shigella and Shiga toxin-producing E. coli. Parasites such as Giardia and Cyclospora cause diarrhea that drags on for weeks; read our article on the Cyclospora stool test if you ate imported produce or traveled recently.
Travelers' diarrhea affects 30% to 70% of travelers during a 2-week trip, mostly from enterotoxigenic E. coli (ETEC).
Clostridioides difficile (C. diff) causes almost half a million infections in the US each year. The risk is up to 10 times higher while taking an antibiotic and stays high for a month afterward, and it rises after age 65.
Medicines and diet
Antibiotics, metformin, magnesium antacids, laxatives and some chemotherapy often cause diarrhea, as do sugar alcohols (sorbitol, mannitol), excess fructose, caffeine and alcohol. Eating patterns matter too, as described in our article on diarrhea after fasting, and hormonal swings explain diarrhea during periods.
Chronic, non-infectious causes
A 2026 JAMA review lists the most common causes of chronic diarrhea that is not due to infection:
- IBS with diarrhea (IBS-D): recurrent belly pain linked to bowel movements. Our irritable bowel syndrome guide covers symptoms and tests.
- Functional diarrhea: more than 25% of stools loose or watery over 3 months, without significant pain.
- Celiac disease: an autoimmune reaction to gluten that damages the small bowel, often with weight loss.
- Bile acid diarrhea: excess bile acids reach the colon and pull water into it, giving frequent, urgent stools.
- Microscopic colitis: inflammation seen only under the microscope; it affects 13% of people with chronic diarrhea.
- Inflammatory bowel disease: Crohn's disease and ulcerative colitis, often with blood, night-time stools or weight loss.
Other causes include small intestinal bacterial overgrowth, lactose intolerance, pancreatic insufficiency (too few digestive enzymes), an overactive thyroid and, less often, colorectal cancer.
Symptoms and warning signs
Cramps, bloating, urgency and nausea are common. The real danger is dehydration. NIDDK lists these signs in adults:
- extreme thirst or dry mouth;
- urinating less than usual, dark-colored urine;
- feeling tired, dizzy or lightheaded;
- skin that does not bounce back quickly when pinched;
- sunken eyes or cheeks.
In infants and young children, also watch for no wet diapers for 3 hours or more, no tears when crying, a sunken soft spot on the skull and drowsiness. Dehydration can also lower blood pressure and make you faint on standing, as our article on dehydration and blood pressure explains.
Red flags that need prompt care include black and tarry stools, red blood or pus in the stool, severe pain in the belly or rectum, frequent vomiting and high fever. For chronic diarrhea, the 2026 JAMA review adds unexplained weight loss, night-time diarrhea, greasy stools, iron deficiency anemia and age 45 or older as reasons for a colonoscopy.
Diagnosis: stool, blood and other tests
Most acute diarrhea needs no test at all. The ACG 2016 guideline on acute diarrheal infections recommends stool testing mainly when there is dysentery (blood and fever), moderate to severe illness, or symptoms lasting more than 7 days. Past 2 weeks, testing becomes useful; our article on which stool tests you need for persistent diarrhea gives the details.
Stool tests
- Multiplex PCR panels: one sample checks for about 20 germs in a few hours, but can also detect germs you carry without being sick.
- C. difficile testing: a PCR or toxin test, done only with 3 or more unformed stools in 24 hours, especially after antibiotics.
- Stool culture: grows the bacterium to test antibiotics; see our guide to the stool culture test.
- Ova and parasites: a microscope exam, useful after travel or well water. Read how to read an ova and parasites report.
- Fecal calprotectin (or lactoferrin): a white blood cell protein that rises with gut inflammation; see our article on the fecal calprotectin test.
- Fecal elastase: a pancreatic enzyme; a low value points to pancreatic insufficiency.
- FIT (fecal immunochemical test): detects hidden blood; a colon cancer screening test, not a diarrhea test.
Blood tests
- Complete blood count (CBC): anemia, high white cells in infection or inflammation. See our complete blood count guide.
- Electrolytes: sodium, potassium, chloride and bicarbonate fall when you lose a lot of stool. Our article on the electrolyte panel explains each value.
- Creatinine and BUN: rise when dehydration reduces blood flow to the kidneys.
- tTG-IgA with total IgA: the screening test for celiac disease, done while you still eat gluten.
- TSH: a low TSH can reveal an overactive thyroid that speeds up the gut.
- CRP, ferritin, albumin: clues to inflammation, iron loss and poor absorption.
The AGA 2019 guideline for chronic watery diarrhea suggests calprotectin or lactoferrin, celiac serology, a Giardia test and testing for bile acid diarrhea. It suggests against routine ova and parasite exams when there is no travel or exposure risk, and against relying on ESR or CRP to rule out IBD.
Endoscopy and imaging
Colonoscopy with random biopsies is the only way to find microscopic colitis, because the colon looks normal. Upper endoscopy with biopsies confirms celiac disease. Scans cannot diagnose pancreatic insufficiency.
Reference values and thresholds
Ranges vary a little between labs. Always compare your result with the range printed on your own report.
| Measure | US units | SI units | What it suggests |
|---|---|---|---|
| Stool frequency | 3 or more loose stools/day | Same | Definition of diarrhea; 6 or more a day: see a doctor |
| Duration | Under 1 week / 2-4 weeks / 4 weeks or more | Same | Acute / persistent / chronic |
| Sodium (blood) | 135-145 mEq/L | 135-145 mmol/L | Low or high values reflect fluid and salt imbalance |
| Potassium (blood) | 3.7-5.2 mEq/L | 3.7-5.2 mmol/L | Often low after heavy or prolonged diarrhea |
| Creatinine (blood) | Men 0.7-1.3 mg/dL; women 0.5-0.95 mg/dL | Men 62-115 µmol/L; women 44-84 µmol/L | A rise can signal dehydration straining the kidneys |
| Fecal calprotectin | 40 µg/g or less | 40 mg/kg or less | 1% or lower probability of IBD in people with IBS symptoms |
| Fecal elastase | Over 200 µg/g normal; 100-200 indeterminate; under 100 µg/g | Same (µg/g = mg/kg) | Under 100 µg/g: good evidence of pancreatic insufficiency |
| C. difficile test | Positive or negative | Same | Meaningful only with 3 or more unformed stools in 24 hours |
How to read your results
A few common patterns help make sense of a report:
- Low potassium, low bicarbonate and high creatinine suggest major fluid loss; our article on the potassium blood test explains the symptoms.
- A positive PCR panel must fit your symptoms: some germs, including C. difficile, are carried without illness.
- A normal calprotectin, a negative tTG-IgA and normal blood counts make IBS-D or functional diarrhea the most likely diagnosis.
- A high calprotectin points to gut inflammation and usually leads to a colonoscopy.
- A positive tTG-IgA suggests celiac disease; our article on the tTG-IgA test explains when a biopsy is still needed.
- A low TSH with diarrhea, weight loss and a fast heartbeat suggests an overactive thyroid; see our TSH blood test guide.
Treatment: how to stop diarrhea safely
Rehydration first
Oral rehydration solution (ORS) is a mix of clean water, sugar and salt. The glucose helps the gut absorb salt and water. For children, the World Health Organization adds a 10 to 14 day course of zinc. Adults with mild diarrhea can also use broths and sports drinks. Older adults and people with diabetes or kidney disease should ask a doctor which ORS to use.
Eating
No strict diet is needed: NIDDK says you can usually return to your normal diet once your appetite comes back, even if diarrhea continues.
Over-the-counter medicines
- Loperamide (Imodium) acts on mu opioid receptors in the gut wall to slow the bowel. For travelers' diarrhea the CDC gives 4 mg first, then 2 mg after each loose stool, never more than 16 mg in 24 hours. Higher doses are dangerous: a 2026 review of 129 overdose cases found severe heart rhythm problems at doses as low as 20 to 40 mg a day.
- Bismuth subsalicylate (Pepto-Bismol) contains a salicylate, an aspirin-like compound. It is not recommended for children under 12, during pregnancy, or for people with an aspirin allergy, gout or kidney failure.
Do not use these medicines alone with bloody stools or fever, nor in infants and children, and see a doctor if diarrhea lasts more than 2 days while taking them.
When antibiotics help
Most community diarrhea is viral, and the ACG guideline discourages antibiotics in most cases. They help in specific situations:
- severe travelers' diarrhea or dysentery: azithromycin is preferred, as a single dose in many cases; rifaximin is an option for non-invasive E. coli;
- C. difficile infection: fidaxomicin, which blocks the bacterium's RNA polymerase, is preferred over vancomycin in the 2021 IDSA/SHEA update, with oral vancomycin an acceptable alternative;
- parasites such as Giardia or Cyclospora, with specific antiparasitic drugs.
Treating chronic diarrhea
Treatment targets the cause: gluten-free diet for celiac disease, bile acid binders such as cholestyramine, pancreatic enzymes, or IBD medicines. For IBS-D and functional diarrhea, the 2026 JAMA review recommends regular meals, exercise, at least 8 cups of non-caffeinated fluids a day, no more than 3 cups of caffeinated drinks, and avoiding alcohol and fizzy drinks. A low-FODMAP diet, loperamide, antispasmodics (hyoscyamine, dicyclomine) or ondansetron improve diarrhea in 50% to 80% of patients.
Prevention
- Wash your hands often with soap and water for at least 20 seconds, as the CDC advises, especially after the bathroom and before cooking.
- When traveling, choose hot, freshly cooked food and sealed drinks. Bismuth subsalicylate cuts travelers' diarrhea by about 50%, but the number of tablets makes it impractical for most trips.
- Take antibiotics only when they are really needed. Every course raises the risk of C. difficile.
- Keep washing your hands and cleaning the bathroom after you recover: you can still spread norovirus for 2 weeks or more after you feel better.
Special populations
Children
NIDDK advises seeing a doctor if diarrhea lasts more than a day, if an infant refuses to eat or drink for more than a few hours, or with any fever in an infant. Call right away for a baby under 12 months or a premature baby. Worldwide, diarrhea still kills about 443,832 children under 5 each year.
Pregnancy
Fluids and ORS are safe and come first. Bismuth subsalicylate should be avoided. Ask your obstetrician before taking loperamide.
Older adults
Adults 65 and older account for most norovirus deaths and have a higher risk of C. difficile. Diuretics and blood pressure medicines worsen dehydration, so checking sodium, potassium and creatinine early is useful.
When to see a doctor
Call 911 or go to the emergency room if you have:
- fainting, confusion, a very fast heartbeat or very little or no urine;
- large amounts of blood, or black and tarry stools;
- severe, constant belly pain or a hard, swollen belly;
- a child who is very drowsy or cannot drink.
Make an appointment soon if:
- diarrhea lasts more than 2 days (adult) or more than 1 day (child);
- you have 6 or more loose stools a day, high fever or frequent vomiting;
- it started during or after antibiotics, a hospital stay or travel abroad;
- it wakes you at night, comes with weight loss, or lasts beyond 4 weeks;
- you are pregnant, over 65, immunocompromised or have kidney disease.
Latest scientific advances in diarrhea
2026: a new JAMA roadmap for chronic diarrhea
An April 2026 JAMA review from Michigan Medicine sets out a simple first step for chronic, non-infectious diarrhea: tTG-IgA with total IgA for celiac disease and fecal calprotectin for IBD. Colonoscopy with random biopsies is advised for red flags or age 45 and older, because microscopic colitis is found in 13% of patients. What it changes for you: a short list of tests can sort most cases, and lifestyle or medicines help 50% to 80% of people with IBS-D or functional diarrhea.
Stool PCR panels: test once, not twice
A 2026 study of 16,502 adults across 12 Cleveland Clinic hospitals and centers found that repeating a panel within 14 days rarely helps. About 24 repeat tests were needed to find one new germ, and 127 to find one that needed antibiotics. What it changes for you: if a first panel is negative and you are still unwell, the next step is usually a different test, not the same panel again.
Microbiome therapies for recurrent C. difficile
In April 2023 the FDA approved Vowst, a capsule of purified bacterial spores taken after antibiotics, to prevent C. difficile from coming back in adults. In its phase 3 trial (NCT03183128), only 12% of treated patients had a recurrence by week 8, compared with 40% on placebo. A 2026 Nature Medicine analysis showed it restores protective gut bacteria, and a 2026 review places Vowst and Rebyota (given rectally) as standard options after a recurrence.
Bile acid diarrhea: recognized more often
A 2026 Chinese expert consensus says bile acid diarrhea is common but often missed or mistaken for IBS-D. A 2026 review notes that the blood test C4 (7α-hydroxy-4-cholesten-3-one) and fecal bile acid tests are promising but still poorly standardized. Bile acid binders remain the main treatment. What it changes for you: if IBS-D treatments fail, ask whether bile acid diarrhea has been tested or tried.
A norovirus vaccine in phase 3
There is still no approved norovirus vaccine. Moderna's mRNA-1403 is being tested in a phase 3 trial of 37,864 adults (NCT06592794), with the main results expected after February 2027. If it works, it could prevent the most common cause of acute diarrhea.
Which tests can help?
For a short bout of diarrhea, you usually need no test. When it lasts beyond 2 weeks, returns often or comes with red flags, a small set of tests answers most questions:
- stool: PCR panel or culture, C. difficile test after antibiotics, ova and parasites after travel, fecal calprotectin, fecal elastase if stools are greasy;
- blood: CBC, electrolytes, creatinine and BUN, tTG-IgA with total IgA, TSH, ferritin and CRP;
- colon cancer screening from age 45 with FIT or colonoscopy, as the USPSTF recommends; a positive FIT test always needs a colonoscopy.
Bring previous results: a trend tells your doctor more than one number.
Glossary
- Bile acid diarrhea: diarrhea caused by too many bile acids reaching the colon.
- Calprotectin: a protein from white blood cells, measured in stool to detect gut inflammation.
- Fecal elastase: a pancreatic enzyme measured in stool to check digestion.
- Microscopic colitis: colon inflammation visible only on biopsy.
- Multiplex PCR panel: a stool test that looks for the genetic material of many germs at once.
- Oral rehydration solution (ORS): a drink of water, sugar and salts that replaces fluid losses.
- tTG-IgA: an antibody blood test used to screen for celiac disease.
Frequently asked questions
What bacteria cause explosive diarrhea?
Sudden, forceful diarrhea often comes from Salmonella, Campylobacter, Shigella, Shiga toxin-producing E. coli or, in travelers, ETEC. Norovirus causes the same picture with vomiting.
What are the treatment options for diarrhea in adults?
Start with fluids and ORS. Loperamide or bismuth subsalicylate can shorten symptoms if there is no blood or fever. Antibiotics are kept for severe travelers' diarrhea, dysentery, C. difficile or parasites.
Why does anxiety cause diarrhea?
The gut and the brain are linked by nerves and stress hormones. Anxiety speeds up bowel contractions and makes the gut more sensitive, which is one reason stress triggers IBS flares. See our article on anxiety. Night-time diarrhea or weight loss point to another cause.
What causes rapid bowel movement after eating?
Eating triggers the gastrocolic reflex, a normal push of the colon. It is stronger in IBS-D, after gallbladder removal, with bile acid diarrhea, after stomach surgery, with an overactive thyroid or with foods you do not tolerate well, such as lactose.
Is diarrhea with no other symptoms for 4 days a concern?
It is often a mild virus or a food or medicine effect, but NIDDK advises seeing a doctor when adult diarrhea lasts more than 2 days.
When should I worry about diarrhea as an adult?
With blood or black stools, high fever, severe pain, dehydration, 6 or more stools a day, diarrhea after antibiotics, or diarrhea beyond 2 days. Beyond 4 weeks, it always needs a work-up.
What is the best medicine for sudden watery diarrhea?
ORS first. Without fever or blood, loperamide (within label limits) or bismuth subsalicylate help adults.
Sources
- Singh P et al. — Chronic, Noninfectious Diarrhea: A Review — JAMA, 2026 — doi.org
- Riddle MS et al. — ACG Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults — American Journal of Gastroenterology, 2016 — doi.org
- Smalley W et al. — AGA Clinical Practice Guidelines on the Laboratory Evaluation of Functional Diarrhea and IBS-D in Adults — Gastroenterology, 2019 — doi.org
- McDonald LC et al. — Clinical Practice Guidelines for Clostridium difficile Infection in Adults and Children: 2017 Update by the IDSA and SHEA — Clinical Infectious Diseases, 2018 — doi.org
- Johnson S et al. — IDSA/SHEA 2021 Focused Update Guidelines on Management of Clostridioides difficile Infection in Adults — Clinical Infectious Diseases, 2021 — doi.org
- Menees SB et al. — A meta-analysis of CRP, ESR, fecal calprotectin and fecal lactoferrin to exclude IBD in adults with IBS — American Journal of Gastroenterology, 2015 — doi.org
- Whitcomb DC et al. — AGA Clinical Practice Update on Exocrine Pancreatic Insufficiency: Expert Review — Gastroenterology, 2023 — doi.org
- Rubio-Tapia A et al. — ACG Guidelines Update: Diagnosis and Management of Celiac Disease — American Journal of Gastroenterology, 2023 — doi.org
- Shu J et al. — Repeat multiplex PCR gastrointestinal panel testing within 14 days yields minimal additional diagnostic information — Infection Control and Hospital Epidemiology, 2026 — doi.org
- Bryant JA et al. — The impact of an oral purified microbiome therapeutic on the gastrointestinal microbiome — Nature Medicine, 2026 — doi.org
- Berry P et al. — FDA-Approved Fecal Microbiota-Based Therapies for Recurrent Clostridioides difficile Infection — Gastroenterology Clinics of North America, 2026 — doi.org
- Chinese Society of Gastroenterology — Chinese Expert Consensus on the Clinical Management of Bile Acid Diarrhea (2026 Version) — Journal of Digestive Diseases, 2026 — doi.org
- Maqsood A et al. — Primary Bile Acid Diarrhea: A Narrative Review of Pathophysiology, Diagnostic Challenges, and Emerging Therapeutic Strategies — Cureus, 2026 — doi.org
- ModernaTX — Phase 3 Study of mRNA-1403 to Prevent Norovirus Acute Gastroenteritis in Adults (NCT06592794) — ClinicalTrials.gov, 2024 — clinicaltrials.gov
- Seres Therapeutics — ECOSPOR III: SER-109 to prevent recurrent C. difficile infection (NCT03183128) — ClinicalTrials.gov, 2017 — clinicaltrials.gov
- Bekka E et al. — Toxicity profile of supratherapeutic loperamide: a systematic review and dose-response analysis — Clinical Toxicology, 2026 — doi.org
- NIDDK — Definition and Facts for Diarrhea — NIH — niddk.nih.gov
- NIDDK — Symptoms and Causes of Diarrhea — NIH — niddk.nih.gov
- NIDDK — Treatment of Diarrhea — NIH — niddk.nih.gov
- CDC — About Norovirus; Norovirus Facts and Stats — CDC — cdc.gov
- CDC — About C. diff — CDC — cdc.gov
- CDC Yellow Book — Travelers' Diarrhea — CDC — cdc.gov
- FDA — VOWST (fecal microbiota spores, live-brpk) — US Food and Drug Administration, 2023 — fda.gov
- WHO — Diarrhoeal disease fact sheet — World Health Organization — who.int
- MedlinePlus — Sodium blood test; Potassium blood test; Creatinine blood test — NLM — medlineplus.gov
- MedlinePlus — Stool Elastase — NLM — medlineplus.gov
- US Preventive Services Task Force — Colorectal Cancer: Screening — USPSTF, 2021 — uspreventiveservicestaskforce.org
Further reading
- Ulcerative colitis blood test: what it shows
- Fecal lactoferrin: what a positive result means
- Gluten intolerance vs celiac disease
- Urine electrolytes: sodium, potassium, FENa
- Creatinine levels: a kidney function guide
- Gut microbiome test: why past drugs matter
- Magnesium levels in blood: how to read results
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