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This article is educational and does not replace your doctor's advice. Seek urgent care for any red-flag symptoms.
What is it?
Diarrhoea means passing three or more loose or watery stools in a day, or more often than is normal for you. It is called acute if it lasts less than 14 days (most often an infection), persistent if it lasts 14 days to 4 weeks, and chronic if it lasts longer than 4 weeks. Lactose intolerance is a different problem that often looks similar: after milk or dairy, a person gets bloating, gas, cramps and loose stools because the small intestine makes too little lactase, the enzyme that digests lactose, the main sugar in milk. A reduced amount of lactase in adulthood (lactase non-persistence) is normal for most adults in the world and does not always cause symptoms. Lactose intolerance is not milk allergy, which is an immune reaction to milk protein and can be dangerous. This article covers food and fluids for both; for causes, tests and medicines please read our articles on diarrhoea and lactose intolerance.
How common is it?
Acute diarrhoea is one of the most common illnesses: adults have it about once a year on average and young children more often. Worldwide it remains a leading cause of death in children under 5, mostly where safe water and sanitation are limited (WHO). Reduced lactase activity affects roughly two thirds of adults worldwide, and it is common in the Middle East, but many people with it have mild or no symptoms and can tolerate some dairy.
Why does it happen?
Acute diarrhoea is usually caused by a virus (such as norovirus or rotavirus), bacteria (such as Salmonella, E. coli or Campylobacter) or parasites, spread by contaminated food or water or from person to person. Medicines (antibiotics, magnesium-containing antacids, metformin and others), food intolerances, and conditions such as irritable bowel syndrome, coeliac disease, inflammatory bowel disease or an overactive thyroid cause longer-lasting diarrhoea. Lactose intolerance is most often due to a gradual, normal fall in lactase after childhood. It can also develop temporarily after a gut infection, or because of coeliac disease or inflammatory bowel disease, and usually improves when that problem is treated. Undigested lactose draws water into the bowel and is fermented by gut bacteria, producing gas and loose stools.
Symptoms
- Loose or watery stools, cramps, urgency and sometimes nausea or fever (infection)
- Thirst, dry mouth, dark urine and tiredness when fluid is being lost
- Bloating, gas, rumbling and cramps from 30 minutes to a few hours after dairy (lactose)
- Loose stools or diarrhoea after milk, ice cream or soft cheese that settle when you avoid them
- Symptoms that vary with the amount of dairy eaten and whether it is taken with other food
Red flags — seek urgent medical care
Signs of dehydration: very little or no urine, dizziness when standing, very dry mouth, sunken eyes, or in babies no wet nappy for several hours, sunken soft spot, sleepiness
Dehydration can become dangerous quickly, especially in babies, older people and pregnancy. Seek urgent medical care.
Blood or pus in the stool, black stools, or a high fever
May be a serious bacterial infection or other disease. See a doctor the same day.
Severe or constant abdominal pain, repeated vomiting so you cannot keep fluids down
Needs urgent assessment; you may need fluids through a drip.
Diarrhoea for more than 2 days in an adult, more than 24 hours in a young child, or more than 14 days for anyone; diarrhoea after antibiotics or a hospital stay
Needs a doctor and possibly stool tests; infections such as C. difficile are possible. Do not simply restrict food further.
Chronic diarrhoea with weight loss, night-time diarrhoea, anaemia, or poor growth in a child
Suggests coeliac disease, inflammatory bowel disease or another condition. Do not self-diagnose lactose intolerance; see a doctor.
After milk: swelling of the lips, face or tongue, wheeze, hives, or collapse; or in a baby, blood in the stool or poor weight gain
This is not lactose intolerance and may be milk allergy. Call emergency services for breathing difficulty or swelling; otherwise see a paediatrician.
How is it diagnosed?
Acute diarrhoea is usually diagnosed from the story and examination, and stool tests are done if it is severe, bloody, long-lasting or follows travel or antibiotics. Chronic diarrhoea needs blood tests, a coeliac blood test, a stool calprotectin test, stool tests and sometimes colonoscopy. Lactose intolerance is suspected from symptoms after dairy. It can be tested by following a lactose-free diet for about 2 weeks and then reintroducing dairy to see if symptoms return, or by a hydrogen breath test, where your breath is measured after a lactose drink. Because the symptoms overlap with irritable bowel syndrome, coeliac disease and inflammatory bowel disease, please do not remove dairy for a long time without proper assessment, especially in children.
What the latest science says
For acute diarrhoea, WHO and the paediatric societies (ESPGHAN/ESPID guideline, 2014) recommend oral rehydration solution (ORS) as the main treatment, continuing feeding (breast milk or formula for babies) and returning to a normal diet early rather than starving or using restricted diets such as BRAT; routine lactose-free formula is not needed. WHO also recommends a 10 to 14 day course of zinc for children with diarrhoea, which shortens the illness. In adults, the ACG guideline on acute diarrhoeal infections (2016) similarly stresses fluid replacement and early eating. Evidence on probiotics for acute diarrhoea is mixed: ESPGHAN (2014) suggested some strains may shorten diarrhoea in children, whereas large North American trials and the AGA probiotic guideline (2020) did not find a benefit, so they are optional. For lactose intolerance, the NIH Consensus Development Conference (2010) concluded that most people with lactose malabsorption can tolerate about 12 grams of lactose (roughly a cup of milk), especially with meals and spread through the day, and warned against unnecessary dairy avoidance because of the effect on calcium and bone health. Yoghurt with live cultures is better tolerated than milk, and lactase enzyme supplements show a modest and inconsistent benefit in trials. Camel milk contains lactose in amounts similar to cow’s milk, and small studies suggesting better tolerance have not been confirmed.
Outlook — what to expect
Most acute diarrhoea settles in a few days with fluids and rest. Lactose intolerance is usually lifelong when it is the normal adult pattern, but it is easily managed by adjusting the amount and type of dairy; when it follows an infection or another disease, it often improves. The main aim in both is to avoid dehydration and keep your nutrition, including calcium and vitamin D, adequate.
Treatment
Habits & Lifestyle
Prevention and hygiene matter as much as diet in infectious diarrhoea.
- Wash your hands with soap and water before preparing and eating food, and after using the toilet or changing nappies.
- Keep cooked food hot or refrigerated; do not leave it out in the heat. Cook meat, poultry and eggs thoroughly, wash fruit and vegetables, and use safe, clean water.
- Avoid raw (unpasteurised) milk of any kind, including camel milk; use pasteurised products.
- Stay away from work or school while you have diarrhoea, and do not prepare food for others until you have been well for at least 48 hours.
- Ask about the rotavirus vaccine for infants, and take care with food and water when travelling.
Diet
In acute diarrhoea, replace fluids first and keep eating. For lactose intolerance, aim to find the amount of lactose you tolerate rather than cutting out dairy altogether.
- Acute diarrhoea, fluids: drink small amounts often. Oral rehydration solution (ORS) is best, because it contains the right balance of salts and sugar; mix the sachet with safe water exactly as the instructions say, and do not add extra sugar or salt. Soups and broths, water and diluted juices also help. Continue breastfeeding or formula in babies. Children and older people need special care.
- Acute diarrhoea, food: do not starve. Start eating as soon as you can, in small frequent meals. Plain starchy foods are usually well tolerated (rice, bread, potatoes, oats, bananas), with eggs, lean chicken, fish, yoghurt and cooked vegetables. A normal diet is the goal; the old BRAT diet (bananas, rice, apples, toast) is too limited to be recommended for more than a short time.
- Acute diarrhoea, avoid for a few days: very fatty, fried or spicy foods; soft drinks, undiluted fruit juice and energy drinks (the sugar can make diarrhoea worse); large amounts of caffeine; and sorbitol sweeteners in sugar-free gum and sweets.
- Acute diarrhoea in children: give ORS and keep feeding; zinc for 10 to 14 days is recommended by WHO and should be given as your paediatrician advises. Do not give anti-diarrhoea medicines to young children, and do not water down milk or formula unless told to.
- Probiotics (yoghurt, laban or capsules) are safe for most healthy people and some may shorten diarrhoea, but the evidence is mixed. They are optional.
- Lactose intolerance, first confirm it: a lactose-free trial of about 2 weeks followed by reintroduction, or a breath test, and have coeliac disease and other causes excluded if symptoms are persistent.
- Lactose intolerance, reduce rather than eliminate: most people can take about 12 g of lactose (roughly a cup of milk) with few or no symptoms. Take dairy in small portions, with meals, spread through the day, and add more gradually to find your own limit.
- Dairy that is often better tolerated: yoghurt with live cultures, laban and ayran, labneh (strained, so lower in lactose), aged hard cheeses (cheddar, parmesan, Swiss), and butter and ghee, which contain only traces of lactose. Fresh soft cheeses, milk, ice cream, cream, milk puddings and evaporated or condensed milk contain more.
- Use lactose-free milk and dairy products, which are nutritionally the same as regular dairy and widely available. Lactase enzyme drops or tablets taken with the first mouthful of dairy help some people, though results vary.
- Check labels for hidden lactose: milk, lactose, whey, curds, milk solids and skimmed-milk powder (in Arabic: حليب، لاكتوز، مصل اللبن، مجفف الحليب). It can be found in bread, biscuits, cakes, sauces, instant soups, processed meats, creamers, protein powders and some tablets.
- Protect calcium and vitamin D: adults need about 1,000 mg of calcium a day (more for women over 50 and men over 70). If you cut dairy, rely on lactose-free dairy, fortified plant milks (soy, oat, almond), canned sardines or fish with soft bones, tahini, almonds, dried figs, broccoli and leafy greens. Vitamin D deficiency is common in Saudi Arabia despite the sunshine, so ask your doctor about testing and a supplement.
- Babies and young children: do not switch formula or remove milk by yourself. If a baby has diarrhoea with blood, vomiting or poor weight gain, it may be milk allergy and needs a paediatrician.
Medications
Medicines are described in our diarrhoea and lactose intolerance articles. In brief:
- Most diarrhoea is viral or self-limiting and antibiotics do not help; use them only when a doctor prescribes them, and never take leftover antibiotics.
- Loperamide can relieve diarrhoea in adults for a short time but should not be used if there is blood in the stool, a high fever, or in young children.
- Some regular medicines cause diarrhoea (metformin, magnesium antacids, antibiotics and others); do not stop them yourself, but ask your doctor.
- For lactose intolerance, lactase enzyme supplements can be used with dairy, as advised by your pharmacist.
Procedures & Surgery
Most people never need a procedure. Your doctor may arrange:
- Stool tests for infection and inflammation, especially if diarrhoea is bloody, severe or lasting.
- A hydrogen breath test for lactose intolerance.
- Colonoscopy or upper endoscopy with biopsies for chronic diarrhoea to look for coeliac disease, inflammatory bowel disease or microscopic colitis.
- Hospital admission and fluids through a drip for severe dehydration.
Living with the condition
- Keep oral rehydration sachets at home and in your travel bag.
- Keep a short note of the dairy foods and amounts you tolerate, and share it with whoever cooks for you.
- Try dairy again from time to time; tolerance can change, and some people find they can take a little more with regular small amounts.
- See a doctor if diarrhoea returns repeatedly or lasts more than a few weeks.
In the Saudi context
Dairy is a big part of Saudi food: laban, yoghurt, labneh, fresh and aged cheeses, camel and cow milk, karak tea made with evaporated milk, milk puddings such as muhalabiya and Umm Ali, and desserts such as kunafa with cheese. Laban, labneh, aged cheese and ghee are usually the easiest to tolerate; karak tea, milk puddings and fresh cheeses contain more lactose, and lactose-free milk can replace regular milk in coffee and desserts. Raw camel milk can carry germs such as brucella and is not recommended; choose pasteurised milk. For diarrhoea, food safety in the heat is important: avoid leaving shawarma, mayonnaise-based sandwiches and salads, rice and meat dishes, and cut fruit out of the fridge for hours; cook eggs and chicken well. Gastroenteritis is common among large crowds, so during Umrah and Hajj wash your hands often, drink bottled or safe water, and eat freshly cooked food. In Ramadan, diarrhoea can cause dehydration quickly: if you have diarrhoea with signs of dehydration, you should not continue fasting, rehydrate with ORS and see a doctor; children and sick people are not required to fast. If you are lactose intolerant, take your dates with lactose-free milk or laban, and choose lactose-free or small portions of dairy at iftar and suhoor.
Questions to ask your doctor
Save this list or print it before your appointment — doctors appreciate prepared patients.
- How do I know if I have lactose intolerance or something else such as coeliac disease or IBS?
- How much dairy can I eat, and which kinds are best for me?
- How do I make sure I get enough calcium and vitamin D?
- When is diarrhoea a reason to see a doctor, and when can I manage at home with ORS?
- What should I do about fasting and diarrhoea in Ramadan, or if my child has diarrhoea?
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Status: Approved for publication by SGA; individual clinician review is ongoing · Published 24/04/2026
For general education only; it does not replace your doctor’s advice. Individual clinician review of this guide is ongoing. SGA clinician? Review this guide