Quick answer
What is food allergy?
A food allergy is when the immune system reacts to a specific food protein, causing symptoms ranging from mild itching and hives to life-threatening anaphylaxis. Common triggers in the UK include peanuts, tree nuts, milk, eggs, wheat, fish, shellfish, sesame, and soy. Diagnosis involves history, skin prick tests, and blood tests. Management is strict avoidance of the trigger food, carrying adrenaline auto-injectors if prescribed, and an allergy action plan.
Food allergy — when eating triggers an immune reaction
A food allergy happens when the immune system mistakenly treats a harmless food protein as a threat, triggering a reaction that can range from mild itching to life-threatening anaphylaxis.
Food allergy is different from food intolerance — intolerance does not involve the same immune pathway and is not immediately dangerous. Getting the distinction right matters for safety and treatment.
Common food allergens in the UK
UK food law requires labelling of 14 major allergens:
- Peanuts and tree nuts (almonds, walnuts, cashews, etc.)
- Milk and eggs
- Fish and shellfish (crustaceans and molluscs)
- Wheat (gluten-containing cereals)
- Soy, sesame, mustard, celery, lupin
- Sulphur dioxide (preservative in dried fruit and wine)
Peanut and tree nut allergies are among the most common causes of severe reactions and often persist for life.
Symptoms
Reactions usually start within minutes to 2 hours of eating.
Mild to moderate:
- Itching in mouth or throat
- Hives (urticaria) — raised itchy welts
- Swelling of lips, face, or eyes
- Vomiting, stomach cramps, diarrhoea
- Runny nose or sneezing
Anaphylaxis — call 999:
- Difficulty breathing or wheezing
- Throat or tongue swelling
- Feeling faint or collapsing
- Rapid heartbeat
- Widespread hives with systemic symptoms
Diagnosis
- Detailed history — what was eaten, how much, how quickly symptoms appeared, and what happened on re-exposure
- Skin prick testing — small amounts of allergen on the skin
- Specific IgE blood tests — measure allergic antibodies
- Oral food challenge — gold standard in specialist settings
Avoid unvalidated tests sold online — IgG food panels are not recommended by NICE for diagnosing allergy.
Management
Strict avoidance of the confirmed allergen — read every label, ask in restaurants, inform schools and workplaces.
Adrenaline auto-injectors — prescribed for people at risk of anaphylaxis. Carry two devices always. Train family and carers to use them.
Allergy action plan — written plan from your allergy team covering symptoms and when to use adrenaline.
Antihistamines — for mild reactions; do not rely on them for anaphylaxis.
Allergen immunotherapy — peanut oral immunotherapy available in specialist NHS centres for selected patients.
Food allergy in children
Milk, egg, wheat, and soy allergies commonly appear in infancy — many children outgrow them by school age.
Peanut, tree nut, fish, and shellfish allergies more often persist.
Early introduction of peanut and egg from around 6 months — in babies who are developmentally ready — may reduce allergy risk, including in infants with eczema. Discuss with your health visitor.
Food allergy vs coeliac disease
Coeliac disease is an autoimmune reaction to gluten — not a classic IgE food allergy. It causes gut damage over time. See coeliac disease for gluten-related illness. See hives for allergic skin reactions.
Common questions
- What is the difference between food allergy and food intolerance?
- Food allergy is an immune system reaction — usually involving IgE antibodies — that can cause rapid, sometimes severe symptoms including anaphylaxis. Food intolerance — such as lactose intolerance — does not involve the immune system in the same way, causes slower symptoms like bloating and diarrhoea, and is not life-threatening.
- What are the symptoms of a food allergy?
- Symptoms usually appear within minutes to 2 hours of eating. Mild to moderate — itching, hives, lip or face swelling, vomiting, diarrhoea, runny nose. Severe (anaphylaxis) — difficulty breathing, throat tightness, wheeze, dizziness, collapse, rapid heartbeat. Anaphylaxis is a medical emergency.
- Which foods most commonly cause allergy in the UK?
- The 14 major allergens regulated in UK food labelling are celery, gluten-containing cereals, crustaceans, eggs, fish, lupin, milk, molluscs, mustard, nuts, peanuts, sesame, soy, and sulphur dioxide. Peanuts and tree nuts cause the most severe reactions in adults and children.
- How is food allergy diagnosed?
- A detailed history of reactions is essential. Allergy specialists use skin prick tests and specific IgE blood tests to identify triggers. Oral food challenges — eating the food under medical supervision — confirm or rule out allergy in some cases. Do not rely on unvalidated commercial tests.
- Can food allergies be cured?
- There is no cure yet. Strict avoidance of the allergen is the mainstay. Some children outgrow milk, egg, wheat, and soy allergies. Peanut and tree nut allergies more often persist. Oral immunotherapy for peanut allergy is available in specialist centres for selected patients.
- What is an adrenaline auto-injector?
- Devices such as EpiPen, Jext, or Emerade deliver a fixed dose of adrenaline (epinephrine) to treat anaphylaxis. People with a history of anaphylaxis or significant allergy should carry two devices at all times. Use at the first sign of anaphylaxis, call 999, and lie flat with legs raised unless vomiting.
- How do I manage food allergy day to day?
- Read food labels carefully — allergens must be highlighted. Inform restaurants and schools. Avoid cross-contamination when cooking. Wear medical alert identification. Follow your allergy action plan. Attend regular allergy clinic follow-up — especially for children.
- Can breastfeeding prevent food allergy in babies?
- Exclusively breastfeeding for around 6 months may reduce eczema risk. Introducing allergenic foods — peanut, egg — from around 6 months in developmentally ready infants may reduce allergy risk, including in babies with eczema. Discuss timing with your health visitor or GP.