Health condition
Allergy vs intolerance
Allergy and intolerance are different mechanisms with different stakes: allergy is immune-driven, rapid and potentially dangerous; intolerance is digestive or chemical, unpleasant but not life-threatening - and the distinction determines testing, treatment and how careful you must be.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
The symptoms to recognise, when to seek help, which specialist to see, and what treatment usually involves.
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Allergy: immune (IgE) reactions within minutes to 2 hours - hives, swelling, vomiting, wheeze, anaphylaxis; even traces can trigger it, and adrenaline auto-injectors may be needed
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Intolerance: dose-dependent digestive symptoms (bloating, pain, wind, diarrhoea) hours later - lactose intolerance and fermentable-carbohydrate (FODMAP) sensitivity are the classic examples; small amounts are often tolerated
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Valid tests: skin prick and specific IgE blood tests for allergy (interpreted against history), hydrogen breath tests or exclusion-reintroduction for intolerance - IgG food panels, hair testing and kinesiology have no scientific validity
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Specialist: a consultant allergist for suspected true allergy; a dietitian for intolerance work - self-imposed exclusion diets without structure impoverish nutrition and often miss the real culprit
Understanding the condition
What it is and what happens next.
What causes it, how it is diagnosed, and the treatment routes available in the UK.
What it is and how it feels
The words are used interchangeably at dinner tables and the distinction could not matter more: food allergy recruits the immune system - IgE antibodies primed against a food protein trigger mast cells within minutes, producing hives, lip and throat swelling, vomiting, wheeze and at worst anaphylaxis, with trace exposures capable of full reactions - while intolerance is a processing problem: missing lactase enzyme leaving milk sugar to ferment, fermentable carbohydrates overwhelming a sensitive gut, or chemical sensitivities to caffeine, histamine-rich foods and additives, all generating genuine misery (bloating, cramps, diarrhoea, headaches) hours later, in proportion to dose, without any capacity to endanger. The history usually separates them - speed, reproducibility, symptom repertoire and the trace-versus-portion question - and the stakes of getting it right run in both directions: an unrecognised allergy is a safety failure, while a mislabelled intolerance sentences someone to needless dietary fear.
Diagnosis and treatment routes
Testing follows the mechanism: suspected allergy warrants allergist assessment with skin prick and specific IgE testing interpreted strictly against the clinical story (unfocused panels breed false positives and phantom allergies), with supervised food challenge as the arbiter and management built on informed avoidance, written emergency plans and adrenaline auto-injectors where indicated; suspected intolerance goes the structured dietary route - hydrogen breath testing for lactose, dietitian-supervised exclusion and staged reintroduction for FODMAPs and other candidates - aiming always at the most liberal diet that controls symptoms, since most intolerances accommodate small amounts and blanket exclusion is both unnecessary and nutritionally costly. The consumer-protection footnote earns its place: IgG food antibody panels, hair analysis and kinesiology-based testing - heavily marketed - measure exposure or nothing at all, and their outputs of long forbidden-food lists have no diagnostic validity; money spent there buys restriction without answers, and the structured pathway above replaces it with both. In many parts of the UK, routine NHS referrals for this kind of problem currently take 20-45+ weeks, whereas an initial appointment with a private consultant is typically available within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a consultant allergist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any of the emergency symptoms described above.
Frequently asked
Common questions about Allergy vs intolerance.
Quick, plain-English answers to what people ask us most.
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What is the difference between a food allergy and a food intolerance?
A food allergy involves the immune system reacting to a specific food protein, potentially causing rapid, sometimes severe reactions including anaphylaxis, while a food intolerance involves difficulty digesting a food, causing uncomfortable but not immune-mediated or life-threatening symptoms.
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What causes food allergies?
Food allergies occur when the immune system mistakenly identifies a food protein as harmful, producing antibodies that trigger the release of histamine and other chemicals on exposure.
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What causes food intolerances?
Intolerances often result from a lack of specific enzymes needed to digest certain foods (like lactase for dairy), sensitivity to food chemicals, or other digestive mechanisms unrelated to the immune system.
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Is a food allergy more dangerous than a food intolerance?
Yes, food allergies can cause severe, rapid, and potentially life-threatening reactions including anaphylaxis, whereas food intolerances typically cause uncomfortable but not immediately dangerous digestive symptoms.
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What are the symptoms of a food allergy versus a food intolerance?
Food allergies can cause hives, swelling, breathing difficulty, and anaphylaxis, often within minutes; food intolerances typically cause bloating, gas, diarrhoea, or stomach pain, usually appearing more gradually and without immune-related symptoms like hives.
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How are food allergies diagnosed?
Diagnosis typically involves skin prick testing, specific blood tests for allergen antibodies, and sometimes a supervised food challenge under medical observation.
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How are food intolerances diagnosed?
Diagnosis often involves an elimination diet followed by structured reintroduction, and sometimes specific tests such as a hydrogen breath test for lactose intolerance.
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Can food intolerances become food allergies, or vice versa?
No, they are fundamentally different mechanisms and one does not typically convert into the other, though someone can certainly have both a true allergy to one food and an intolerance to a different food.
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Is testing for food intolerance always reliable?
Some commercially available food intolerance tests lack strong scientific validation, so it's best to seek assessment from a doctor, dietitian, or allergist for a properly evidence-based approach to diagnosis.
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When should I see a doctor about a suspected food allergy or intolerance, and how quickly can I be seen privately?
See a doctor promptly for suspected food allergy, especially with any history of severe reaction. NHS allergy referral can take several weeks, while private allergy or dietetic assessment is often available within about one to two weeks.