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Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Yes, usually. A doctor can assess your symptoms by video and plan a trial without lactose; breath tests and tests for other causes are done in person.
- What it is: a digestive problem in which the body does not make enough lactase, the enzyme that digests lactose, the sugar in milk.
- When symptoms start: soon after, or within a few hours of, food or drink that contains lactose.
- How much is tolerated: most people with lactose intolerance can have up to 12 g of lactose at once, about a cup of milk, with no or minor symptoms.
- Emergency: call 112 if your lips, mouth, throat or tongue suddenly swell or you struggle to breathe after food: that is an allergic reaction, not lactose intolerance.
Lactose intolerance does not damage the body. Call 112 if, after food or drink, your lips, mouth, throat or tongue suddenly swell, you are struggling to breathe or swallow, your skin or lips turn blue, grey or pale, or you become very confused, drowsy or faint. These are signs of a severe allergic reaction.
Can an online doctor treat lactose intolerance?
Yes, usually. Lactose intolerance is recognised from your symptoms and how they relate to dairy, and it is managed by changing how much lactose you have, which works well by video. The doctor checks for warning signs and other causes, such as coeliac disease or IBS, plans a trial without lactose, and advises on lactase supplements, calcium and vitamin D. A hydrogen breath test, blood tests and tests for other conditions are done in person, and the doctor tells you when they are needed.
How an online consultation helps with lactose intolerance
- Is it really lactose?: The pattern after dairy is checked, and so are other causes, such as IBS or coeliac disease.
- A trial that gives an answer: Cutting down lactose for a while shows whether it is the cause.
- Your bones protected: Calcium and vitamin D advice when you cut down on dairy.
- The right tests: When a breath test, blood tests or a referral are needed.
What the doctor checks in an online lactose intolerance consultation
The doctor checks for signs of another cause first. The doctor asks about:
- Warning signs: blood in your poo, weight loss without trying, or changes in your poo that have lasted 3 weeks.
- Your symptoms: wind, bloating, rumbling, cramps, diarrhoea or constipation, and how soon after dairy they start.
- What sets them off: milk, ice cream, soft cheese, and processed foods with hidden milk.
- When it started: after a stomach bug, a new diagnosis, bowel surgery or cancer treatment, or gradually over years.
- Your health: coeliac disease, Crohn’s disease or IBS, pregnancy, and the medicines you take, some of which contain lactose.
Before the call, keep a food and symptom diary for a week if you can: what you ate and drank, when, and what happened afterwards.
What is lactose intolerance?
Lactose is the natural sugar in milk. To digest it, the small intestine makes an enzyme called lactase. When there is not enough lactase, lactose passes undigested into the large bowel, where bacteria break it down and cause wind, bloating and diarrhoea. Low lactase without symptoms is called lactose malabsorption; only people with symptoms are lactose intolerant.
It is not an allergy. A food intolerance does not involve the immune system, and lactose does not damage the body, while a milk allergy can be life-threatening.
How common is lactose intolerance?
About 65 to 68% of people worldwide have a reduced ability to digest lactose after infancy, and in Africa and Asia most people do. It is least common in people with European ancestry: only about 5% of people of northern European descent lose their lactase.
What are the symptoms of lactose intolerance?
Symptoms start soon after, or within a few hours of, food or drink that contains lactose. Small amounts often cause none. They include:
- tummy pain and cramps
- bloating
- wind (farting) and a rumbling tummy
- diarrhoea or, in some people, constipation
- feeling or being sick
How do I know if I am lactose intolerant?
The clue is a pattern: the same symptoms after milk, ice cream or soft cheese, and fewer of them when you cut down. Keep a food and symptom diary, then, with a doctor’s advice, try cutting out lactose for a while. If your symptoms improve, lactose intolerance is likely.
Why have I suddenly become lactose intolerant?
Lactose intolerance can start at any age. There are two common reasons it seems to appear suddenly:
- Your lactase has fallen over the years. In most people worldwide, lactase drops after infancy, and symptoms may not begin until later childhood, the teenage years or early adulthood. This is called lactase non-persistence, and it is the most common cause.
- Something has injured the small intestine. A bowel infection such as a stomach bug, coeliac disease, Crohn’s disease, bowel surgery, or radiotherapy or chemotherapy can lower lactase. This is secondary lactose intolerance, and it can improve once the cause is treated, although that can take time.
Other conditions cause similar symptoms after food, especially IBS and coeliac disease, so new symptoms are worth checking, particularly with weight loss or blood in your poo.
Lactose intolerance, milk allergy or IBS?
These three are often confused, but they behave differently and need different care:
Swipe sideways to compare →
| What differs | Lactose intolerance | Cow’s milk allergy | IBS |
|---|---|---|---|
| What it is | Too little lactase to digest milk sugar | An immune reaction to milk | A long-term condition of how the gut works |
| Typical symptoms | Wind, bloating, cramps and diarrhoea after lactose | Itchy skin or a raised rash, swelling of the lips, face and eyes, wheezing or difficulty breathing | Cramps, bloating, diarrhoea or constipation, with many triggers |
| Timing | Soon after, or within a few hours | Straight after the food, or days later | Often worse after eating, better after a poo |
| Is it dangerous? | No: lactose does not damage the body | It can be life-threatening | Usually lifelong, but lifestyle changes and medicine help |
| What helps | Less lactose, lactose-free products, lactase supplements | Avoiding milk, with tests and advice from an allergy specialist | Diet and lifestyle changes, and medicine for symptoms |
How is lactose intolerance diagnosed?
Most people are diagnosed from their symptoms and a trial without lactose. If the answer is unclear, a doctor may arrange:
- A lactose elimination diet: you stop having lactose for a while to see whether your symptoms improve.
- A hydrogen breath test: you have a drink containing lactose, and the hydrogen in your breath is measured to show how well you digest it.
- Blood tests: to look for other causes, such as coeliac disease.
- A gastroscopy: a camera test of the stomach and upper bowel, if symptoms are severe and do not improve.
Do not cut foods out of your diet long term without advice from a doctor or dietitian.
What foods contain lactose?
Lactose is in milk from cows, goats and sheep and in foods made from it, and it is often added to processed food:
Swipe sideways to compare →
| Group | Examples | What to know |
|---|---|---|
| Main sources | Milk and ice cream | Most likely to cause symptoms |
| Lower in lactose | Yoghurt, and hard cheeses such as cheddar or Swiss | Often manageable in small amounts |
| Hidden lactose | Breakfast cereals, baked goods, sauces, dressings, diet and protein shakes, and packaged or ready meals | Look for milk, whey, curds and dry milk solids on the label |
| Medicines | Some tablets contain small amounts of lactose | Ask the pharmacist if even small amounts affect you |
| Lactose-free | Lactose-free milk and other lactose-free or lactose-reduced dairy | A way to keep dairy in your diet |
Reading labels in Europe
Across the EU, milk, including lactose, is one of 14 allergens that must be declared on food, and it must be highlighted in the ingredients list by its font, style or background colour. That makes milk easy to spot on packaged food wherever you shop in the EU.
How much lactose can you have?
Most people with lactose intolerance do not need to cut out dairy completely. The European Food Safety Authority found that most can have up to 12 g of lactose at once, about the amount in a cup of milk, with no or minor symptoms, and more when it is spread through the day:
- Have milk in small amounts, and with meals.
- Try yoghurt and hard cheeses, which are lower in lactose.
- Use lactose-free milk and dairy products.
- Take a lactase supplement before food or drink that contains lactose, if it helps you.
Calcium and vitamin D
Milk and dairy are the most common sources of calcium, and vitamin D helps the body absorb and use it. If you cut down, get calcium from lactose-free dairy, fish with soft bones, leafy greens, almonds and tofu, and vitamin D from eggs, fish such as salmon, and fortified foods. Ask the doctor whether you need a supplement.
What happens if you ignore lactose intolerance?
Lactose does not damage the body, so having it causes symptoms but no lasting harm. The real risks are cutting out dairy without replacing its calcium and vitamin D, and missing another cause of your symptoms, such as coeliac disease.
Which lactose intolerance treatment might the doctor recommend?
Lactose intolerance is managed with diet, and the plan depends on the cause and on what else is going on. This is the framework the doctors use:
Swipe sideways to compare →
| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| Wind, bloating or diarrhoea after milk, otherwise well | A food diary and a trial of cutting down lactose | Yes | Not usually needed |
| Symptoms that started after a stomach bug | Less lactose while the gut recovers | Yes | If diarrhoea lasts more than a few days |
| Not sure whether dairy is the cause | A food diary, and sometimes a hydrogen breath test | Yes, to plan | For the breath test |
| Symptoms with weight loss, blood in your poo or anaemia | Tests for coeliac disease, IBD and other causes | Partly | For blood tests and specialist tests |
| Cutting out dairy and worried about your bones | Calcium and vitamin D advice, and supplements if needed | Yes | Not usually needed |
| Swelling of the lips or tongue, or difficulty breathing after food | Emergency care for an allergic reaction | No | Call 112 now |
Is dairy really the cause of your symptoms? A doctor can help you find out in one consultation.
See available times →Treatment options for lactose intolerance
What you can do yourself
- Keep a food and symptom diary to find how much lactose you can manage.
- Have dairy in smaller amounts, spread through the day and with meals.
- Choose lactose-free milk, and check labels for milk, whey and curds.
- Try a lactase supplement before meals that contain lactose.
- Keep your calcium and vitamin D up from other foods.
Prescription treatment
A prescription is never issued without a consultation. Lactose intolerance is managed with diet rather than medicine. The doctor may prescribe calcium and vitamin D when your diet falls short, and treats or refers you for any underlying cause, such as coeliac disease. If the doctor prescribes, use the prescription at a pharmacy near you.
What does not help
Cutting out all dairy for good without advice, which can leave you short of calcium. Assuming every symptom after food is lactose: IBS and coeliac disease cause similar symptoms and need different care.
Special situations
After a stomach bug or traveller’s diarrhoea
A bowel infection can lower lactase for a while. Cutting down on lactose until your gut recovers can help; see travellers’ diarrhoea and gastroenteritis.
Coeliac disease or Crohn’s disease
Lactose intolerance is more likely while the small intestine is damaged, and it can improve as the gut heals. Treating the underlying condition comes first.
Pregnancy and breastfeeding
Tell the doctor if you are pregnant or breastfeeding, so your calcium and vitamin D can be checked before you cut down dairy.
Children
Mobi Doctor consultations are for adults aged 18 and over. A child who is unwell needs a paediatrician or a local doctor in person, and emergency signs in a child mean 112.
When lactose intolerance is treated online, and when you need in-person care
Treated online: recognising lactose intolerance, planning a trial without lactose, advice on how much dairy you can manage, lactase supplements, calcium and vitamin D, and symptoms after a stomach bug.
In-person care: a hydrogen breath test, blood tests and other tests for coeliac disease or inflammatory bowel disease, a gastroscopy, and any severe allergic reaction.
When to get in-person care
Call 112 or go to an emergency department now for:
- sudden swelling of the lips, mouth, throat or tongue
- breathing very fast or struggling to breathe, a tight throat, or struggling to swallow
- skin, tongue or lips that turn blue, grey or pale
- sudden confusion, drowsiness or dizziness, or fainting
Get medical advice the same day for:
- bleeding from your bottom, or bloody diarrhoea
- diarrhoea that lasts more than a few days
See a doctor if symptoms keep coming back after eating, or you have had looser poo, constipation, bloating or blood in your poo for 3 weeks, or you are losing weight without trying.
How Mobi Doctor works
- Book a time that suits you: daily 7am–11pm CEST. You can see a doctor over video, usually within 15 minutes. No subscription, and the exact price is shown before you pay.
- Speak to a licensed doctor about your symptoms: say what you eat and drink, when the symptoms come on, and whether anything has changed, such as a recent stomach bug.
- Leave with a plan: what to do, what to take and for how long, and which signs mean you should be seen in person. If the doctor prescribes, use the prescription at a pharmacy near you.
No sign-up needed
Not sure it’s lactose intolerance? Tick every symptom you have to see each condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call.
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Similar symptoms, different condition? Irritable Bowel Syndrome (IBS) can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about lactose intolerance
What is lactose intolerance?
A digestive problem in which the body does not make enough lactase, the enzyme that digests lactose, the sugar in milk. Undigested lactose causes wind, bloating, cramps and diarrhoea.
What are the symptoms of lactose intolerance?
Tummy pain and cramps, bloating, wind, a rumbling tummy, diarrhoea or sometimes constipation, and feeling or being sick, after food or drink that contains lactose.
How soon after dairy do symptoms start?
Lactose intolerance symptoms start soon after, or within a few hours of, food or drink that contains lactose, typically 30 minutes to 2 hours later, as the undigested sugar reaches the large bowel and ferments; the bigger the dose, the sooner and stronger the wind, bloating and diarrhoea. Small amounts often cause no symptoms at all, and lactose taken with a meal is tolerated better than milk on an empty stomach.
Why am I suddenly lactose intolerant?
Lactose intolerance often appears later because lactase levels fall over the years in most people, so symptoms can start in the teens or adulthood. A stomach bug, coeliac disease, Crohn’s disease, bowel surgery or cancer treatment can also lower lactase, sometimes for a while only.
How do I know if I am lactose intolerant?
Look for the same symptoms after milk or soft cheese that ease when you cut down. A food diary and a trial without lactose usually give the answer, and a hydrogen breath test can confirm it.
Is lactose intolerance an allergy?
No. An intolerance does not involve the immune system and does not damage the body. A milk allergy is an immune reaction that can cause swelling and difficulty breathing, and it can be life-threatening.
Is it lactose intolerance or something else?
Lactose intolerance is wind, bloating and loose stools within hours of milk, ice cream or soft cheese, with relief when they are avoided and no symptoms from hard cheese or lactose-free milk. A milk allergy causes hives, swelling or wheeze quickly after even tiny amounts and can be dangerous; coeliac disease causes similar gut symptoms but from gluten, with tiredness and anaemia; IBS brings bloating and changed bowels unrelated to dairy; and a hydrogen breath test settles it.
What foods should I avoid if I am lactose intolerant?
Milk and ice cream are the main sources. Yoghurt and hard cheeses contain less lactose and are often fine in small amounts. Check labels for milk, whey and curds in processed foods.
Can lactose intolerance cause constipation?
Yes. Diarrhoea, wind and bloating are the best-known symptoms of lactose intolerance, but a minority of people get constipation instead, probably because the gases produced by fermentation slow the bowel in some people; the pattern, symptoms after dairy and relief without it, is the clue either way. Constipation with blood, weight loss or a change that persists for 3 weeks needs assessment rather than a dairy-free diet.
What happens if you ignore lactose intolerance?
Lactose does not damage the body, so it causes symptoms but no lasting harm. The risks are going short of calcium and vitamin D if you cut out dairy, and missing another cause such as coeliac disease.
How long does lactose intolerance last?
Lactose intolerance that comes on with age is usually lifelong, because lactase does not return, but the symptoms are fully controllable by matching dairy to your limit and using lactase drops or tablets; lactose intolerance after a stomach bug, coeliac disease or a course of antibiotics is often temporary and clears within a few weeks to months as the gut lining heals. Symptoms of one episode settle within hours to a day once the lactose has passed through.
How can I stop lactose intolerance symptoms quickly at home?
There is no quick fix once symptoms have started. To prevent them, have smaller amounts with meals, choose lactose-free products, or take a lactase supplement first. Severe or lasting symptoms need a doctor.
Can an online doctor help with lactose intolerance?
Yes, usually. A doctor can assess your symptoms by video, rule out warning signs, plan a trial without lactose and advise on calcium and vitamin D. Breath tests and blood tests are done in person.
- Lactose intolerance, NHS, National Health Service (UK), reviewed 8 July 2026.
- Definition and facts for lactose intolerance, NIDDK, US National Institutes of Health, reviewed February 2018.
- Symptoms and causes of lactose intolerance, NIDDK, US National Institutes of Health, reviewed February 2018.
- Eating, diet and nutrition for lactose intolerance, NIDDK, US National Institutes of Health, reviewed February 2018.
- Lactose intolerance: symptoms and causes, Mayo Clinic, updated 22 September 2025.
- Lactose intolerance, MedlinePlus Genetics, US National Library of Medicine, updated 24 March 2023.
- Scientific opinion on lactose thresholds in lactose intolerance and galactosaemia, EFSA Panel on Dietetic Products, Nutrition and Allergies, EFSA Journal, 2010.
- Food allergy, NHS, National Health Service (UK), reviewed 20 August 2026.
- Coeliac disease: complications, NHS, National Health Service (UK), reviewed 31 March 2023.
- Irritable bowel syndrome (IBS), NHS, National Health Service (UK), accessed 15 October 2026.
- Irritable bowel syndrome (IBS): symptoms, NHS, National Health Service (UK), reviewed 17 March 2025.
- Stomach ache, NHS, National Health Service (UK), reviewed 26 May 2023.
- List of 14 allergens, Food Safety Authority of Ireland, 2026.
- Regulation (EU) No 1169/2011 on the provision of food information to consumers, European Union, EUR-Lex, 25 October 2011.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
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