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Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Partly. A doctor can go through a reaction, find the likely food and plan what to do next; allergy tests and anaphylaxis care are in person.
- What it is: the immune system overreacting to a food, usually a protein in it, from a few minutes to a few hours after eating.
- How common: about 6% of UK adults, around 2.4 million people, have a confirmed food allergy, and about half started in adulthood.
- Most common in adults: peanuts, tree nuts, and fresh fruits such as apple, peach and kiwi linked to pollen allergy.
- Emergency: call 112 for swelling of the lips, mouth, throat or tongue, difficulty breathing or swallowing, or feeling faint.
Do not book a video appointment if your lips, mouth, throat or tongue suddenly swell after eating, you are struggling to breathe or swallow, your throat feels tight, or you feel faint, confused or drowsy. Use an adrenaline auto-injector if you have one and call 112.
Can an online doctor help with a food allergy?
Partly. A doctor by video can go through a reaction to food in detail, which is the most important part of diagnosing a food allergy, narrow down the likely food, recommend antihistamines for mild reactions, and explain the signs of anaphylaxis and what to do. Confirming the allergy needs tests at an allergy clinic, such as skin prick tests, blood tests or a supervised food challenge, and the doctor arranges the referral.
How an online consultation helps with a food allergy
- The likely food found: From what you ate, how much, and how quickly the symptoms started.
- Allergy or intolerance: Two different problems, with different risks and different tests.
- A plan for next time: Antihistamines for mild reactions, and the signs that mean adrenaline and 112.
- The right tests: A referral for tests that work, and a warning about the ones that do not.
What the doctor checks in an online consultation for a food allergy
The doctor asks about the reaction in detail, because a careful history is the basis of every food allergy diagnosis. The doctor asks about:
- Warning signs: any swelling of the throat or tongue, breathing difficulty or faintness, now or during the reaction.
- The food: what you ate, how much, whether it was raw or cooked, and whether you have eaten it before without problems.
- The timing: how long after eating the symptoms started, and how long they lasted.
- The symptoms: hives, swelling, itching in the mouth, tummy pain, being sick, diarrhoea, sneezing or wheezing.
- Other allergies: hay fever, asthma and eczema, and allergies in your family.
- Anything else at the time: exercise, alcohol, medicines and illness.
Before the call, write down exactly what you ate in the hours before the reaction, keep any food labels, and take photos of any rash or swelling.
What is a food allergy?
A food allergy is the immune system overreacting to a food, usually a protein in it, as if it were a threat. Most food allergies are immediate, called IgE-mediated, and cause symptoms within about 2 hours of eating. Some are delayed, called non-IgE-mediated, and cause symptoms hours or even days later. An extremely small amount of the food can be enough to cause a reaction.
How common are food allergies in adults?
About 6% of adults in the UK, around 2.4 million people, have a clinically confirmed food allergy. Many more, over 30% of adults, report reactions to some foods, which is why proper testing matters. Food allergy is not only a childhood problem: around half of adult food allergies start in adulthood.
What are the symptoms of a food allergy?
Itchy skin or hives, swelling of the lips, face and eyes, tingling or itching in the mouth, feeling or being sick, tummy pain, diarrhoea, sneezing, a runny nose, coughing or wheezing, and feeling dizzy. Severe reactions affect the airway, breathing or circulation, and are anaphylaxis.
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| Severity | What you notice | What to do |
|---|---|---|
| Mild to moderate | Hives, swelling of the lips, face or eyes, itching or tingling in the mouth, tummy pain, being sick, diarrhoea | Antihistamine, and see a doctor |
| Severe (anaphylaxis) | Swelling of the throat or tongue, difficulty breathing or swallowing, wheezing, feeling faint, confusion, blue or pale skin | Adrenaline auto-injector, and call 112 |
How long after eating does a reaction start?
Immediate reactions usually start soon after eating, often in the first few minutes and within 2 hours. Delayed reactions can start hours or days later.
How long does a food allergy reaction last?
Mild reactions such as hives usually get better within a few days. Anaphylaxis always needs emergency care, even if the symptoms ease. See anaphylaxis.
What are the most common food allergies?
Any food can cause an allergy, but food law in the UK names 14 major allergens that must be highlighted on labels:
- celery
- cereals containing gluten, such as wheat, rye, barley and oats
- crustaceans, such as prawns, crabs and lobsters
- eggs
- fish
- lupin
- milk
- molluscs, such as mussels and oysters
- mustard
- peanuts
- sesame
- soybeans
- sulphur dioxide and sulphites, above ten parts per million
- tree nuts, such as almonds, hazelnuts, walnuts, Brazil nuts, cashews, pecans, pistachios and macadamia nuts
In adults, peanuts and tree nuts are the most likely to cause a reaction. Many adults also react to fresh fruits such as apple, peach and kiwi, which is linked to birch pollen allergy and called pollen food syndrome. See nut allergy and oral allergy syndrome.
Shellfish allergy
Shellfish come in two groups: crustaceans, such as prawns, crab, lobster and crayfish, and molluscs, such as mussels, oysters, scallops, squid and octopus. Reacting to one shellfish makes a reaction to others in the same group likely, and a reaction to the other group is possible. A few people with a serious shellfish allergy react to the vapours while it is being cooked. Shellfish allergy does not mean an allergy to the iodine in X-ray contrast dye: the reaction is to a muscle protein, not iodine.
Fish allergy
People allergic to one fish have a high chance of reacting to others, because they contain similar proteins, but fish allergy does not raise the risk of shellfish allergy. It often starts in childhood and may be lifelong, but it can also start in adulthood. Some people react to vapours from fish being cooked. Two lookalikes: scombroid poisoning, from histamine in fish such as tuna and mackerel that has started to spoil, can affect anyone; and a parasite in some fish and shellfish, called anisakis, can cause allergic reactions.
Sesame allergy
Sesame is one of the 14 major allergens. People allergic to both peanuts and tree nuts may be more likely to be allergic to sesame too, and should ask their specialist.
Food allergy or food intolerance?
They are different problems. A food allergy involves the immune system and can cause anaphylaxis. A food intolerance does not involve the immune system: it causes symptoms such as bloating and tummy pain, usually a few hours after eating, and is not an allergy.
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| Food allergy | Food intolerance | |
|---|---|---|
| Immune system | Involved | Not involved |
| Typical symptoms | Hives, swelling, itching in the mouth, wheezing, being sick | Bloating, tummy pain |
| Timing | Usually within 2 hours; some delayed types later | Usually a few hours after eating |
| Can cause anaphylaxis? | Yes | No |
| Valid tests | Skin prick, blood tests, food challenge | Cutting the food out and reintroducing it |
See lactose intolerance and coeliac disease, a reaction to gluten that is different from both.
How is a food allergy diagnosed?
A food allergy needs a specialist to diagnose it, starting from a careful account of the reaction. The tests that work are:
- Skin prick test: a drop of the food extract pricked into the skin, done under medical supervision.
- Blood test: measures specific IgE antibodies to the food.
- Food challenge: the food given in gradually increasing amounts under medical supervision, with resuscitation equipment available.
- Cutting out and reintroducing the food: for delayed allergies, where skin and blood tests do not help, ideally with a dietitian.
A positive skin or blood test on its own does not prove an allergy: it has to fit the story of what happened. See allergy testing.
Are food intolerance tests reliable?
Not the ones sold online and on the high street. IgG blood tests are not reliable, because healthy people without food allergies have IgG antibodies to foods too. Vega or electrodermal tests, kinesiology, hair analysis and pulse tests have no scientific basis. They can lead to unnecessary, restrictive diets and nutritional deficiencies, or miss a real allergy.
Living with a food allergy
Avoid the food completely, including as an ingredient, read labels every time, take an antihistamine for mild reactions, and carry adrenaline if you have been prescribed it.
- Labels: the 14 major allergens must be highlighted in the ingredients list of pre-packed food. Food prepacked for direct sale, packed on the premises where it is sold, must show a full ingredients list.
- “May contain” labels: these warn that an allergen may be present unintentionally. There is no legal requirement to use them, so their absence does not prove a food is safe.
- Eating out: restaurants, cafés and takeaways must give you allergen information. Check the menu or call ahead, be clear about your allergy, ask about cross-contamination and recipe changes, and if you doubt the staff understand, do not eat there.
- Mild reactions: a non-drowsy antihistamine.
- Severe reactions: an adrenaline auto-injector, or an adrenaline nasal spray, then call 112. Carry 2 doses at all times if they have been prescribed.
- An allergy action plan: from your specialist, so the people around you know what to do.
Can a food allergy be cured?
Avoiding the food is the main treatment. Children with a peanut allergy may be offered immunotherapy, but they still avoid peanuts.
Can a food allergy go away over time?
Sometimes, mainly in children: about 1 in 5 to 1 in 10 children are thought to outgrow a nut allergy, usually by the age of 4 or 5. Many childhood food allergies persist into adulthood, so regular reviews with a specialist check whether yours has changed. Never test it yourself by eating the food.
What might the doctor recommend for a reaction to food?
What happens next depends on the reaction, how severe it was and the likely food. This is the framework the doctors use:
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| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| Throat or tongue swelling, breathing difficulty, or feeling faint after eating | Adrenaline and emergency treatment | No | Call 112 now |
| Hives or swollen lips after a food, with normal breathing | Antihistamine, avoiding the food, and a referral | Yes, to assess | Allergy tests at a specialist clinic |
| Itching in the mouth with raw fruit or nuts | Assessment for pollen food syndrome | Yes | Tests if the reactions go beyond the mouth |
| Bloating or tummy pain hours after certain foods | Assessment for intolerance or other gut problems | Yes | Tests if the doctor suspects coeliac disease or another condition |
| A reaction to fish or shellfish you have eaten before | Assessment, including for spoiled fish and parasites | Partly | Allergy tests |
| A diagnosed food allergy, needing a review | A check of your plan and your auto-injectors | Yes | Regular specialist reviews |
Reacted to something you ate? A doctor can go through it and plan the next steps in one consultation.
See available times →Special situations
Asthma and food allergy
Asthma raises the risk of a severe allergic reaction, so keep it well controlled and carry 2 auto-injectors if you have been prescribed them. See asthma.
Pregnancy and breastfeeding
Speak to a doctor or pharmacist before taking an antihistamine: loratadine is usually recommended if you need one in pregnancy.
A strange reaction to red meat
Hives or anaphylaxis 2 to 6 hours after eating beef, pork or lamb can be alpha-gal syndrome, linked to tick bites. See alpha-gal syndrome.
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 a food allergy is treated online, and when you need in-person care
Treated online: going through a reaction to food, narrowing down the likely food, telling allergy from intolerance, antihistamines for mild reactions, a plan for next time, and referral to an allergy specialist.
In-person care: anaphylaxis, skin prick tests, blood tests and food challenges, and immunotherapy.
When to get in-person care
Use an adrenaline auto-injector if you have one, and call 112 now for:
- sudden swelling of the lips, mouth, throat or tongue
- fast or difficult breathing, or wheezing
- a tight throat or trouble swallowing
- skin, lips or tongue turning blue, grey or pale
- sudden confusion, drowsiness or dizziness, or fainting
Get medical advice the same day for:
- hives, itching or swelling of the lips or face after eating, with normal breathing
- a first reaction to a food you had eaten before without problems
- vomiting or diarrhoea after eating that will not settle
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 the reaction: say what you ate, how much, how soon the symptoms started, and what they were.
- Leave with a plan: what to avoid, what to do if it happens again, which tests to have, 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 a food allergy? 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. If you have an emergency sign listed on this page, call 112 instead.
Tap the body — an area or a point — to browse symptoms anywhere
Similar symptoms, different condition? Lactose Intolerance can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about food allergy
What is a food allergy?
A food allergy is the immune system overreacting to a food, usually a protein in it. It causes symptoms such as hives, swelling and being sick, usually soon after eating, and can cause anaphylaxis.
What are the most common food allergies in adults?
Peanuts and tree nuts are the most likely to cause reactions. Many adults also react to fresh fruits such as apple, peach and kiwi, linked to birch pollen allergy.
What causes a food allergy?
A food allergy happens when the immune system mistakes a protein in a food for a threat and makes IgE antibodies against it, so the next time you eat the food, histamine and other chemicals are released. Why this happens is not fully understood: allergies, asthma and eczema in the family, eczema in infancy, and pollen allergy, which cross-reacts with raw fruit and nuts, all raise the risk, and adults can develop a new food allergy at any age.
What are the 14 major allergens?
Celery, cereals containing gluten, crustaceans, eggs, fish, lupin, milk, molluscs, mustard, peanuts, sesame, soybeans, sulphites and tree nuts. They must be highlighted on food labels, because they cause most food allergy reactions.
What is the difference between a food allergy and a food intolerance?
A food allergy involves the immune system and can cause anaphylaxis. A food intolerance does not involve the immune system and causes symptoms such as bloating and tummy pain, usually a few hours after eating.
Can you develop a food allergy as an adult?
Yes. Around half of adult food allergies start in adulthood, and a food you have eaten for years can suddenly cause hives, swelling or sickness; fish, shellfish, peanuts, tree nuts and wheat are among the foods that begin causing allergy in adults. Pollen-related reactions to raw fruit and vegetables, oral allergy syndrome, also usually start in adults with hay fever.
How long after eating does an allergic reaction start?
Immediate food allergy reactions usually start soon after eating, within 2 hours and often much sooner, with hives, swelling, tingling in the mouth or sickness; the faster and more widespread the reaction, the more likely it is to become severe. Delayed reactions, which mostly affect the gut and skin, can start hours or even days later, which makes the food harder to pin down.
Can a food allergy go away over time?
Sometimes, mainly in children, but many childhood food allergies persist into adulthood. A specialist can check whether yours has changed; never test it yourself by eating the food.
How is a food allergy diagnosed?
By a specialist, from your account of the reaction plus skin prick tests, blood tests or a supervised food challenge. A positive test on its own does not prove an allergy.
How can I prevent a food allergy reaction?
Once a food allergy is confirmed, avoid the food completely: read every label, since the 14 major allergens must be highlighted, ask about ingredients and cross-contamination when eating out, and be careful with buffets, bakeries and takeaways. Carry a non-drowsy antihistamine, and an adrenaline auto-injector if one has been prescribed, keep asthma well controlled, and tell the people you eat with what to do. Do not cut out foods you only suspect without a proper assessment, because unnecessary avoidance has costs of its own.
Are food intolerance tests reliable?
No. IgG blood tests, Vega tests, kinesiology and hair analysis have no scientific basis for diagnosing food allergy or intolerance, and can lead to unnecessary diets.
If I am allergic to shellfish, can I have iodine contrast dye?
Yes. Shellfish allergy does not predict a reaction to iodine contrast dye, because the allergy is to a muscle protein in shellfish, tropomyosin, not to iodine, and iodine itself is not an allergen. Tell the radiology team about any previous reaction to contrast dye, which is a separate matter, but a shellfish food allergy on its own is not a reason to avoid a scan.
Can a food allergy be cured?
Not yet. Avoiding the food is the main treatment for a food allergy, with an antihistamine for mild reactions and an adrenaline auto-injector if there is a risk of anaphylaxis. Children with a peanut allergy may be offered oral immunotherapy, which raises the amount they can tolerate but means they still avoid peanuts in everyday life, and some allergies, especially to milk and egg, are outgrown in childhood.
Can an online doctor help with a food allergy?
Partly. A doctor can go through a reaction, find the likely food and plan what to do next. Allergy tests and anaphylaxis care are in person.
- Food allergy, NHS, National Health Service (UK), reviewed 20 August 2026.
- Around 6% of the UK adult population have a food allergy, Food Standards Agency (UK), updated 16 May 2024.
- Food allergy and intolerance advice for consumers, Food Standards Agency (UK), updated 7 August 2026.
- Food allergy and food intolerance, BDA, British Dietetic Association, food fact sheet, reviewed March 2024.
- Food allergy and food intolerance testing, BDA, British Dietetic Association, food fact sheet, August 2026.
- Shellfish allergy, Anaphylaxis UK, factsheet, accessed 15 October 2026.
- Fish allergy, Anaphylaxis UK, factsheet, updated September 2026.
- Peanut and tree nut allergy, Anaphylaxis UK, factsheet, accessed 15 October 2026.
- Evidence-based versus non-evidence-based allergy tests and treatments, ASCIA, Australasian Society of Clinical Immunology and Allergy, March 2024.
- Hives, NHS, National Health Service (UK), reviewed 26 April 2024.
- Alpha-gal syndrome, UKHSA, UK Health Security Agency, updated 12 January 2026.
- Emergency treatment of anaphylaxis, Resuscitation Council UK, guideline, May 2021.
- Antihistamines, NHS, National Health Service (UK), reviewed 16 May 2023.
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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