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Diarrhoea: causes, what helps and when to see a doctor
Watery stools, abdominal cramps, the feeling that you might not make it to the next toilet: almost everyone gets acute diarrhoea several times in their life. Most of the time it is a harmless gastrointestinal infection that clears up in two to three days. But sometimes diarrhoea is a warning sign – of food poisoning, an antibiotic side effect or a chronic bowel disease. Here you will learn what really helps, when loperamide makes sense and when you should see a doctor.
If there is bloody stool, high fever, severe dehydration or diarrhoea in babies, seek medical help immediately!
1. What you can do right now
Quick help for acute diarrhoea
Drink: plenty of fluids – ideally an oral rehydration solution (ORS) from the pharmacy. Water, unsweetened tea or clear broth are alternatives.
Bland food: rusks, boiled rice, banana, grated apple, carrot soup – easy to digest.
Avoid irritants: no alcohol, no coffee, no fatty food, no raw food.
Loperamide: only useful for short-term use in acute diarrhoea without fever and without blood in the stool – not for children under 12.
Check medications: antibiotics, metformin, magnesium supplements and NSAIDs can cause diarrhoea.
See a doctor immediately!
See a doctor immediately if there is bloody or black stool, high fever (above 39 °C), severe abdominal pain, signs of dehydration (dark urine, dizziness, skin folds that don't snap back), or diarrhoea in babies, small children or older people. In the case of acute circulatory collapse, call 112!
2. Understanding diarrhoea – what is happening in the body?
We speak of diarrhoea when stools are unformed, watery or pasty and passed more than three times a day. Diarrhoea is not a disease in its own right but a symptom – the causes range from harmless gastrointestinal infections to chronic bowel diseases.
Acute diarrhoea (less than two weeks) is usually triggered by gastrointestinal infections, spoiled food or medications. If diarrhoea lasts longer than four weeks, doctors speak of chronic diarrhoea – and it is worth looking for a specific cause. In both cases the key is: the body must get enough fluids and electrolytes, otherwise dangerous dehydration may occur.
Simple self-test: skin pinch test and urine colour
If you pinch a fold of skin on the back of your hand and it stays standing instead of snapping back immediately, that is a sign of fluid deficit. Dark yellow, strongly smelling urine and a dry mouth also indicate dehydration – then drink more, ideally an ORS.
3. Common causes of diarrhoea
3.1 Acute diarrhoea (less than two weeks)
Gastrointestinal infection (gastroenteritis): by far the most common cause. Viruses (especially noroviruses, rotaviruses) or bacteria (e.g. salmonella, campylobacter, E. coli) cause watery stools, nausea, vomiting and abdominal cramps. Colloquially known as stomach flu.
Food poisoning: food contaminated with bacterial toxins (e.g. Staphylococcus aureus, Bacillus cereus). Symptoms often begin within a few hours of eating.
Travellers' diarrhoea: bacterial infection caused by unfamiliar germs in drinking water or food – affects a substantial proportion of all long-distance travellers. More: medications when travelling.
Stress and excitement: acute stress can speed up bowel movements and cause diarrhoea – often underestimated.
Alcohol: irritates the intestinal lining and disrupts water absorption in the gut.
3.2 Chronic diarrhoea (over four weeks)
Irritable bowel syndrome: the most common cause of chronic diarrhoea in young adults. A functional bowel disorder with changing stool patterns, bloating and abdominal cramps.
Inflammatory bowel disease:Crohn's disease and ulcerative colitis – usually with bloody or mucous diarrhoea, abdominal pain and weight loss.
Coeliac disease: gluten intolerance – diarrhoea, bloating, fatigue and signs of nutrient deficiency. Often only recognised late.
Hyperthyroidism: speeds up bowel transit and can cause chronic diarrhoea.
Microscopic colitis: a frequently overlooked cause of watery chronic diarrhoea, especially in older women. The intestinal lining looks normal during colonoscopy – only a tissue sample reveals the inflammation.
4. Diarrhoea in children and babies
In babies and small children, diarrhoea must be taken particularly seriously because their small bodies dehydrate faster than adults. Watch for the following signs of dehydration: dry nappy (fewer than six wet nappies a day in babies), sunken fontanelle, dry lips, listlessness or crying without tears.
Oral rehydration solutions (ORS) from the pharmacy are the treatment of choice – not cola, not salty pretzels. Breastfeeding or bottle feeding should be continued during the diarrhoea. Loperamide is generally not recommended for children under twelve. For babies under six months with diarrhoea, always see a doctor.
Babies and small children: when in doubt, see a doctor
In babies and small children, dehydration can become dangerous within just a few hours. Better to see a paediatrician or go to the emergency department once too often than too late.
5. Treating diarrhoea – what really helps
Fluids and electrolytes
The most important thing in diarrhoea. Drink plenty of water, unsweetened tea or clear broth. For more severe or persistent diarrhoea, oral rehydration solutions (glucose-electrolyte mixtures) from the pharmacy are useful – they replace water, salts and sugar in the right composition.
Bland food
Easy-to-digest foods like rusks, boiled rice, grated apple, bananas, carrot soup or toast. The old BRAT diet (banana, rice, apple, toast) is not strictly evidence-based but does no harm. More important than the choice of foods is adequate fluid intake.
What to avoid?
Very fatty foods, raw food, alcohol, coffee, dairy products (if lactose intolerance is suspected) and very sugary or carbonated drinks can make the diarrhoea worse.
Cola and salty pretzels are not recommended
The old tip is outdated: cola contains too much sugar and too little sodium, and salty pretzels only provide sodium without potassium. Oral rehydration solutions from the pharmacy are much better – they have the right ratio of water, salts and glucose.
6. Could it be your medication?
Medications are a common, often underestimated cause of diarrhoea – and some active ingredients help against it. The most important at a glance:
Medication
Effect on diarrhoea
Antibiotics
The most common drug-related cause – change the gut flora, in rare cases Clostridioides difficile infection possible
Metformin (diabetes)
Common side effect, especially at the start of therapy – usually decreases over time
Magnesium supplements
Can cause watery diarrhoea, especially at higher doses
Loperamide
Inhibits bowel movement – helpful short-term in acute diarrhoea without fever/blood, not for children under 12
Table can be scrolled to the right
Caution: Clostridioides difficile
Severe, persistent diarrhoea (more than three times a day) during or up to eight weeks after antibiotic therapy, with fever, abdominal pain or foul-smelling stool, can indicate a C. difficile infection. Particularly dangerous for older, hospitalised or immunocompromised people – have it checked by a doctor promptly.
Digital medication plan: record all your medications – your family doctor, gastroenterologist and pharmacy can immediately see which active substances may cause diarrhoea. → Create a medication plan
Interaction check: antibiotics and the pill? Loperamide and opioids? Check interactions. → Start the interaction check
Reminder for taking medication: take loperamide, probiotics or prescribed medications regularly. → Set up a reminder
The most important thing with diarrhoea is adequate fluid intake – ideally with oral rehydration solutions (ORS) from the pharmacy. Bland food (rice, rusks, banana) and rest support recovery. Loperamide can help short-term in acute diarrhoea without fever.
Diarrhoea is dangerous when signs of dehydration appear (dark urine, dizziness, dry mouth), with bloody or black stools, with high fever, in babies and small children, in older or immunocompromised people, or with severe diarrhoea while on antibiotics.
Acute diarrhoea usually subsides within two to three days. If it lasts more than three days without improvement, it should be checked by a doctor. From four weeks onwards we speak of chronic diarrhoea, which needs to be investigated systematically.
Loperamide can help short-term in acute diarrhoea without fever and without blood in the stool. It should not be taken if there is fever, bloody stools or suspected bacterial infection. Loperamide is generally not recommended for children under twelve.
No – this tip is outdated and not recommended. Cola contains too much sugar and too little sodium, and salty pretzels do not provide potassium. Oral rehydration solutions from the pharmacy replace water and electrolytes in the right composition.
Antibiotics change the gut flora and can therefore cause watery diarrhoea. Mostly harmless. In rare cases Clostridioides difficile can spread – severe diarrhoea with fever during or after antibiotics requires prompt medical attention.
Certain probiotics (e.g. Saccharomyces boulardii, Lactobacillus rhamnosus GG) can shorten the duration of diarrhoea in gastroenteritis. The evidence applies to specific strains – not all probiotics are equivalent. Particularly useful for antibiotic-associated diarrhoea.
Diarrhoea that lasts longer than four weeks. Requires systematic investigation – common causes are irritable bowel syndrome, inflammatory bowel diseases, coeliac disease, food intolerances or medication side effects.
Sources
DGVS S2k guideline on gastrointestinal infections and Whipple's disease (AWMF 021-024, 2023)
gesundheitsinformation.de (IQWiG): diarrhoea
RKI – gastroenteritis guide
German Society for Gastroenterology, Digestive and Metabolic Diseases (DGVS)
brite app: anonymised user data, as of April 2026
Medical disclaimer: This page is for general information and is not a substitute for medical advice, diagnosis or therapy. If warning signs occur such as blood in the stool, high fever, severe dehydration or diarrhoea in children and older people, seek medical help immediately. Loperamide must not be taken in cases of fever or bloody diarrhoea. Last updated: April 2026.
If there is bloody stool, high fever, severe dehydration or diarrhoea in babies, seek medical help immediately!
