Food Allergy vs Food Intolerance
Understanding the difference between food allergy and food intolerance can make a real difference to how you manage your symptoms. This guide covers what each condition is, how they are diagnosed, and what you can do about them. Written by Ghislaine Swinburn, HCPC-registered dietitian.
Food Allergy
An immune system reaction to a food protein. Even a tiny amount can trigger symptoms. Reactions can be immediate and, in severe cases, life-threatening (anaphylaxis).
Food Intolerance
A digestive or metabolic response to a food — not immune-mediated. Symptoms are usually dose-dependent and delayed, and are rarely life-threatening.
How They Work: The Mechanisms
Food Allergy
Involves the immune system — specifically IgE antibodies (in IgE-mediated allergy) or other immune pathways (in non-IgE-mediated allergy). The body mistakenly identifies a food protein as a threat and mounts an immune response. This can affect multiple body systems simultaneously.
Food Intolerance
Does not involve the immune system. Instead, it may result from enzyme deficiencies (such as lactase deficiency in lactose intolerance), sensitivity to food chemicals (such as histamine or salicylates), or the fermentation of certain carbohydrates in the gut (as in FODMAP sensitivity).
Symptoms
| Food Allergy | Food Intolerance | |
|---|---|---|
| Onset | Usually within minutes–2 hours | Often delayed (hours or days) |
| Amount needed | Tiny amounts can trigger reaction | Usually dose-dependent |
| Severity | Can be life-threatening | Rarely life-threatening |
| Systems affected | Skin, gut, airways, cardiovascular | Mainly digestive |
| Common symptoms | Hives, swelling, vomiting, anaphylaxis | Bloating, diarrhoea, stomach pain, fatigue |
Diagnosis
IgE-Mediated Food Allergy
Diagnosed by an allergy specialist, usually through skin prick testing, specific IgE blood tests, or an oral food challenge under medical supervision. A detailed clinical history is essential.
Non-IgE-Mediated Food Allergy
Does not show up on standard allergy tests such as skin prick testing or IgE blood tests. Diagnosis is made through a structured elimination and reintroduction diet, guided by a dietitian, alongside a detailed clinical history. This type of allergy is more common in infants and young children and often affects the gut.
Food Intolerance
Often identified through a structured elimination and reintroduction diet, guided by a dietitian. Some intolerances (such as lactose intolerance) can be confirmed with a hydrogen breath test.
Unvalidated tests — not recommended
Hair testing and IgG antibody tests are not validated diagnostic tools and are not recommended by allergy or dietetic professional bodies. If you have received results from one of these tests, I can help you make sense of your symptoms using evidence-based approaches instead.
Management
Food Allergy
- Strict avoidance of the trigger food
- Carrying emergency medication (e.g. adrenaline auto-injector) if prescribed
- Allergy action plan from your specialist
- Dietitian support to ensure nutritional adequacy while avoiding trigger foods
Food Intolerance
- Identifying trigger foods through a structured dietary approach
- Understanding your personal threshold — many intolerances are dose-dependent
- Avoiding unnecessary restriction — the goal is the widest possible diet you can comfortably manage
- Dietitian support to guide the process and protect nutritional balance
A Note on Unvalidated Tests
Many commercial tests claim to identify food allergies or intolerances — including IgG antibody tests, hair analysis, and kinesiology. These tests are not supported by clinical evidence and are not recommended by allergy or dietetic professional bodies.
If you have received results from one of these tests and are unsure what to do next, I can help you make sense of your symptoms using evidence-based approaches.
In Summary
Food allergy and food intolerance are different conditions with different mechanisms, symptoms, and management approaches. Getting the right diagnosis matters — both to keep you safe and to avoid unnecessary dietary restriction. A dietitian can help you navigate the process with clarity and confidence.
Need personalised support?
Whether you’re managing a confirmed allergy or trying to understand your symptoms, I can help you find clarity and build a diet that works for you.