Diarrhea: causes, what to do and when to see a doctor

In short

• Diarrhea is loose, watery stools three or more times a day, or more often than is normal for you.
• Most acute cases come from a viral or food-borne infection and go away on their own. The main risk is dehydration.
• Treatment at home is to replace fluids and electrolytes, with water, broth or an oral rehydration solution, and to go back to normal eating as soon as you feel like it.
• Over-the-counter anti-diarrhea medicine can suit some adults but not infants, children, or anyone with a fever or bloody stools.
• Get medical help for signs of dehydration, black or bloody stools, severe pain, a high fever, or diarrhea lasting more than 2 days in adults and more than a day in children.

What diarrhea is and what causes it

Diarrhea is a symptom, not a disease. MedlinePlus describes acute diarrhea as the common short-lived kind, and chronic diarrhea as lasting at least four weeks and sometimes pointing to an underlying condition.

According to the NIDDK, acute diarrhea is most often caused by:

The danger is rarely the diarrhea itself. It is the loss of body water and salts, called dehydration, which can become serious, particularly for children, older adults and people with weakened immune systems. That is why fluids come before everything else.

• Viral gastroenteritis, from viruses such as norovirus, rotavirus, adenovirus or astrovirus.
• Food poisoning from bacteria such as Salmonella, Campylobacter, E. coli, Staphylococcus aureus or C. perfringens.
• Travelers' diarrhea, picked up from contaminated food or water.
• Medicines, including antibiotics, magnesium-containing antacids, cancer drugs and liquid medicines that contain sugar alcohols.

Longer-lasting diarrhea has a wider list of causes. These include food intolerances such as lactose, celiac disease, Crohn's disease, ulcerative colitis, irritable bowel syndrome and surgery on the stomach or abdomen. When diarrhea clears within a few days, finding the exact cause is usually unnecessary.

Symptoms: usual and worrying

Typical symptoms are the loose stools themselves, an urgent need to reach a bathroom, cramping or belly pain and nausea. Loss of bowel control can happen.

Some infections add warning features:

• Bloody stools, or black, tarry or pus-containing stools.
• Fever, chills, lightheadedness or dizziness.
• Frequent vomiting that stops you keeping fluids down.
• Signs of dehydration: extreme thirst, a dry mouth, little urine, dark urine, fatigue, dizziness, skin that stays pinched after release, and sunken eyes or cheeks.
• In young children, also no wet diapers for 3 hours or more, no tears when crying, a sunken soft spot on the head and unusual sleepiness.

What to do right now

1. Drink early and oftenTake small, frequent sips of water, broth or an oral rehydration solution. These solutions are sold without a prescription and are designed to replace both fluid and electrolytes.
2. Eat when you feel like itYou do not need to fast. Return to your normal diet as your appetite comes back, adding soft, bland foods first if that feels better.
3. Avoid what irritates the gutSkip alcohol, caffeine, fried and other high-fat food, sugar-free candy and gum, and large amounts of sugary drinks and juices while it settles.
4. Think before using a medicineLoperamide or bismuth subsalicylate can be used by many adults for acute diarrhea, but ask a pharmacist first and read the label. Do not use them for children, or when there is a fever or blood in the stool.
5. Protect other peopleWash your hands with soap and water often, do not prepare food for others and avoid sharing towels until you are well.
6. Know your limitIf you cannot keep fluids down, notice dehydration signs, or have any warning symptom from the list above, contact a clinician.

How to tell it from look-alike conditions

• Viral gastroenteritis: the usual cause of an acute stomach bug. It often brings vomiting as well, and the NHS says vomiting typically settles in a day or two.
• Food poisoning: symptoms follow a particular meal, and other people who ate it may be ill too. Some infections cause bloody stools or fever, which is a reason to be examined.
• Medicine-related diarrhea: starts after a new medicine, particularly an antibiotic. A long course of antibiotics can lead to C. difficile infection.
• Food intolerance, such as lactose: loose stools, gas and bloating follow particular foods and recur each time you eat them.
• Chronic bowel conditions: irritable bowel syndrome, celiac disease, Crohn's disease and ulcerative colitis cause diarrhea that comes and goes or lasts for weeks, and chronic diarrhea can cause weight loss.

When to see a doctor

Contact a health care professional right away for any of these, at any age: confusion, irritability or lethargy; frequent vomiting; severe abdominal or rectal pain; black, tarry, bloody or pus-containing stools; or any sign of dehydration.

Adults should also call if diarrhea lasts more than 2 days, if there is a high fever, or if there are six or more loose stools in a day. A fever of 102°F or higher is the usual cut-off. For children, call if diarrhea lasts more than a day, and do not wait with newborns and infants. Infants under 12 months, premature babies, children with other medical conditions and children who cannot keep up with fluids need prompt care.

Call 911 if a person is confused, faints, stops urinating, has a rapid heartbeat or rapid breathing, or seems to be going into shock. Severe dehydration may need IV fluids in a hospital.

Before you call, note when it started, how many loose stools you have had, whether you have seen blood, your temperature, any recent travel or new medicine, and how much fluid you have kept down. These details help the clinician decide quickly how urgent your case is.

How a clinician finds the cause and treats it

The clinician asks how long you have had diarrhea, what your stools look like, what you eat and drink, which medicines you take, and whether you have travelled recently. The exam looks for fever and dehydration, listens to the abdomen and compares your weight with earlier records. If needed, the tests are:

• A stool test for blood, bacteria, parasites or signs of disease.
• Blood tests, which can reveal signs of certain causes or complications such as dehydration.
• A colonoscopy, which lets the doctor view the inside of the digestive tract.
• Other tests, such as a hydrogen breath test, or a trial change of diet.

When diarrhea lasts less than 7 days, a doctor typically does not need to look for the cause. Longer episodes, or episodes with other symptoms, are more likely to be investigated.

Treatment follows the cause. Fluids and electrolytes come first, and severe dehydration may require IV fluids. Antibiotics may help with some digestive tract infections, so the clinician decides case by case whether you need one. Chronic causes such as inflammatory bowel disease need prescription treatment, and food intolerances are managed by avoiding the trigger foods. The NIDDK notes that evidence does not clearly support probiotics for diarrhea.

Preventing spread at home

Diarrheal infections pass easily from person to person, so a few habits protect the rest of the household.

• Wash your hands with soap and water after using the toilet and before handling food.
• Clean toilets, taps and other frequently touched surfaces every day.
• Do not share towels, washcloths or utensils.
• Wash soiled clothing and bedding separately on a hot cycle.
• Avoid preparing food for other people while you are unwell.

Children, pregnancy and older adults

• Babies and young children: dehydration can develop within a day or two in infants. Keep up breast milk or formula, use oral rehydration solution as advised, and avoid over-the-counter diarrhea medicines unless a doctor says otherwise. Check with a doctor before giving an infant a rehydration solution.
• Older children: keep their usual age-appropriate diet and offer fluids often.
• Pregnancy: people who are pregnant are at higher risk of complications, so call a clinician earlier.
• Adults over 65, people with weakened immune systems and people taking antibiotics: also at higher risk of complications.
• People with diabetes, kidney disease or other chronic conditions: check with a doctor about fluids and medicines before treating yourself.

Myths and facts

• Myth: you should stop eating until it passes. Fact: most experts do not recommend fasting or a restricted diet beyond avoiding irritating foods.
• Myth: every case is food poisoning. Fact: viral gastroenteritis is the leading cause of acute diarrhea.
• Myth: an antibiotic speeds recovery. Fact: antibiotics may help with some infections only, and most acute diarrhea is viral.
• Myth: stopping the diarrhea quickly is always the goal. Fact: replacing fluids matters more, and medicines that slow the gut are unsuitable when there is a fever or blood in the stool.

Questions and answers

Sources

1. NIDDK — Symptoms & Causes of Diarrhea
2. NIDDK — Diagnosis of Diarrhea
3. NIDDK — Treatment for Diarrhea
4. NIDDK — Eating, Diet & Nutrition for Diarrhea
5. MedlinePlus — Diarrhea
6. MedlinePlus — Dehydration
7. NHS — Diarrhoea and vomiting

Sources checked on 30 October 2026.