What Is a Food Allergy?
A food allergy is an immune-system reaction to a specific food protein. When someone with a food allergy consumes the trigger food, their immune system recognises the protein as a threat and mounts a rapid IgE-mediated response. This response releases histamine and other chemicals that cause the characteristic allergic symptoms.
Key features of a true food allergy:
- Fast onset: Symptoms typically appear within minutes and up to two hours of eating the trigger food
- Immune-mediated: Involves IgE antibodies — measurable in a blood test
- Dose-independent: Even a tiny amount of the allergen can trigger a reaction in sensitised individuals
- Reproducible: The same food reliably triggers the same response
- Potentially serious: Severe allergic reactions (anaphylaxis) are a medical emergency
Common food allergens in the UK: Peanuts, tree nuts (cashew, walnut, hazelnut), sesame, milk, egg, wheat, fish, shellfish, soy. The 14 major allergens must be declared on food labels under UK law.
What Is Food Intolerance?
Food intolerance is a fundamentally different condition. It is not IgE-mediated, does not involve the allergy arm of the immune system, and poses no risk of anaphylaxis. Instead, intolerances are typically:
- Delayed: Symptoms may appear hours to days after eating the trigger food, making the connection hard to identify
- Dose-dependent: Small amounts may be tolerated; larger amounts cause symptoms
- Gut-focused: Bloating, gas, abdominal pain, and diarrhoea are typical
- Variable: Can depend on overall gut health, stress, and other factors
Lactose intolerance — the inability to digest the milk sugar lactose due to insufficient lactase enzyme — is the most common example. Non-coeliac gluten sensitivity and fructose malabsorption are other examples. These are metabolic or functional issues, not immune responses.
Why IgG Food Intolerance Tests Are Not Recommended
Commercial IgG food intolerance tests are widely marketed — but they are not endorsed by any major allergy or immunology body, and the science does not support them.
IgG antibodies to foods are a normal finding in anyone who has eaten those foods regularly. Having IgG antibodies to wheat does not mean you are intolerant to wheat — it means your immune system has been exposed to wheat, which is expected. Using IgG levels to determine a "personalised" list of foods to avoid typically results in unnecessary restriction with no clinical benefit.
The British Society for Allergy and Clinical Immunology (BSACI), the British Dietetic Association, and the European Academy of Allergy and Clinical Immunology (EAACI) all advise against IgG food testing for the investigation of food intolerance.
What ALEX3 Actually Tests For
ALEX3 (Allergy Explorer 3) is a validated multiplex IgE testing platform that measures specific IgE antibodies to over 300 allergen components — including food allergens, pollen, pet dander, house dust mite, mould, and venom.
ALEX3 is a test for IgE-mediated allergy only. It is the most comprehensive validated blood test available for identifying true allergies, and it provides molecular component-level precision that standard RAST tests cannot match. It does not detect, diagnose, or measure food intolerance.
| Food Allergy | Food Intolerance | |
|---|---|---|
| Mechanism | IgE-mediated immune response | Non-immune (enzyme, gut) |
| Onset | Minutes to 2 hours | Hours to days |
| Dose | Tiny amounts trigger reaction | Usually dose-dependent |
| Risk | Anaphylaxis possible | Not life-threatening |
| Blood test | ALEX3 / specific IgE | No validated test exists |
| Diagnosis | IgE testing, skin prick, GP assessment | Elimination diet, clinical history |
Which Test Do You Need?
If you experience immediate reactions after eating — hives, swelling, vomiting, breathing difficulty within two hours of eating — a food allergy is the more likely diagnosis, and ALEX3 testing is appropriate.
If you experience delayed digestive symptoms — bloating, gas, abdominal pain hours after eating — food intolerance is more likely. The appropriate approach is a structured elimination diet with GP or dietitian guidance, not a blood test.
If you are unsure, book a GP appointment to discuss your symptoms. Our GP will take a clinical history and advise on the right investigative approach.