Food Allergy vs Intolerance: The Complete Guide to the Difference

Food allergy and food intolerance are regularly confused, including by people who have one of the two conditions. The mechanisms, severity, and management implications are genuinely different — and the distinction matters practically when you are communicating with a caterer, a restaurant, or a food business. Using the wrong term can result in a food business treating a serious medical need as a preference, with consequences that range from discomfort to a medical emergency.

How a food allergy works

A food allergy is an immune system response. The immune system identifies a specific food protein as a threat and produces antibodies against it. On subsequent exposures, those antibodies trigger an immune response that can be rapid and severe.

IgE-mediated food allergies — the type most commonly associated with severe reactions — produce symptoms within minutes to two hours of exposure. These include hives and skin flushing, swelling (including of the throat), vomiting, difficulty breathing, and in the most severe cases anaphylaxis: a systemic reaction that can be life-threatening without prompt treatment with adrenaline. People diagnosed with a food allergy at anaphylaxis risk are prescribed an adrenaline auto-injector (such as an EpiPen or Jext) and should carry it at all times.

Non-IgE-mediated allergies produce slower reactions — typically over hours rather than minutes — and primarily affect the gut and skin. These are harder to diagnose because the delayed response makes it less obvious which food caused the reaction.

The critical feature of a food allergy is that it is not dose-dependent in the way intolerance tends to be. Trace amounts — amounts too small to taste or even measure in a normal kitchen context — can be sufficient to trigger a serious reaction in a sensitised individual. This is why cross-contamination in a kitchen or in manufacturing is not a minor concern for someone with a diagnosed food allergy.

How a food intolerance works

A food intolerance is a non-immune response. The body reacts to a food substance, but the mechanism does not involve the immune system producing antibodies. The most common mechanisms are enzyme deficiency (lactose intolerance, for example, occurs when the body does not produce sufficient lactase to digest the milk sugar lactose) and pharmacological reaction to naturally occurring food chemicals.

Non-coeliac gluten sensitivity is a recognised condition in which gluten causes gastrointestinal and other symptoms in the absence of the autoimmune intestinal damage that defines coeliac disease. The mechanisms are not fully understood, and there is no validated diagnostic test — it is typically diagnosed by exclusion after coeliac disease and wheat allergy have been ruled out.

Intolerances are generally dose-dependent: many people with lactose intolerance, for instance, can tolerate small amounts of dairy without significant symptoms. This is a meaningful practical difference from an allergy, where trace exposure carries real risk.

Food intolerances are rarely life-threatening, but they significantly affect quality of life when unmanaged. They deserve to be taken seriously, both by the person managing them and by food businesses catering for them.

Coeliac disease: neither allergy nor intolerance

Coeliac disease does not fit neatly into either category. It is an autoimmune condition in which gluten triggers an immune response that damages the lining of the small intestine — but it is not an IgE-mediated allergy and it does not cause anaphylaxis. The damage is cumulative and ongoing: even small amounts of gluten cause intestinal damage in someone with coeliac disease, even when there are no obvious symptoms. This means coeliac disease requires the same strict avoidance as a diagnosed food allergy, not the more flexible management appropriate to an intolerance.

The distinction matters when briefing a caterer. Someone with coeliac disease saying "I have a gluten intolerance" may lead a food business to treat the request with less rigour than the situation warrants. "I have diagnosed coeliac disease and need strict gluten avoidance" communicates the medical reality more accurately.

Why the distinction matters when commissioning catering

When an office manager or event organiser communicates dietary requirements to a caterer, the framing affects the response. A well-run food business will ask clarifying questions — but many will not. Providing accurate information from the start produces better outcomes.

For someone with a diagnosed IgE-mediated food allergy, the information to communicate is:

The specific allergen (not just "nut allergy" — specify peanuts, tree nuts, or both; specify which tree nuts if known)
That this is a diagnosed allergy, not a preference or intolerance
Whether the person carries an adrenaline auto-injector (this indicates the severity of their diagnosis)
Whether the allergy is to trace exposure or requires only avoidance of the ingredient as a component

For someone with coeliac disease:

State the diagnosis explicitly — coeliac disease, not gluten-free preference
Ask for confirmation that gluten-free items are prepared on dedicated equipment, or ask honestly whether the kitchen handles gluten
Request the allergen matrix and check every item individually

For someone with a food intolerance that does not carry serious medical risk:

Communicate the intolerance clearly, but understand that a caterer may not be able to guarantee complete absence of the relevant substance
Clarify your individual tolerance threshold if relevant — whether, for example, you can eat food cooked in butter even if you avoid milk as a standalone ingredient

Diagnosis and professional support

Food allergy diagnosis involves clinical assessment: skin prick tests, specific IgE blood tests, and in some cases supervised oral food challenges conducted in a clinical setting. Self-diagnosis from food diaries alone is unreliable and can result in unnecessary restriction of nutritious foods. Allergy UK (allergyuk.org) and the British Society for Allergy and Clinical Immunology (bsaci.org) provide authoritative guidance on navigating allergy diagnosis and management.

Food intolerance management often benefits from dietitian-supervised protocols — the low-FODMAP diet for IBS-related intolerances, for instance, is a structured elimination and reintroduction process rather than a permanent blanket restriction. Unnecessary long-term restriction of food groups without clinical guidance can lead to nutritional deficiencies.

Coeliac disease diagnosis requires a GP referral for blood testing followed by intestinal biopsy. Anyone considering testing should continue eating gluten until the process is complete — removing gluten before testing allows the intestine to heal and can produce a false negative result. Coeliac UK (coeliac.org.uk) provides detailed guidance on the diagnostic pathway.

For genuinely allergen-safe catering across London — independently halal-certified, 100% nut-free and fully allergen-labelled under Natasha’s Law — browse our catering shop or WhatsApp the kitchen.

Frequently asked questions

What is the practical difference between a food allergy and a food intolerance for a caterer to know about?

A food allergy involves an immune response that can cause severe or life-threatening reactions at trace exposure — cross-contamination is a real medical risk. A food intolerance is typically dose-dependent and non-immune: small amounts may be tolerated and reactions are generally not life-threatening. The practical implication for catering is that an allergy requires strict avoidance and rigorous cross-contamination management; an intolerance requires clear labelling and honest communication about ingredients.

Is coeliac disease an allergy or an intolerance?

Neither, strictly — it is an autoimmune condition. Gluten triggers an immune response that causes intestinal damage, even without obvious symptoms and even at trace amounts. It is not an IgE-mediated allergy (so anaphylaxis is not the risk), but it requires the same strict avoidance as a diagnosed food allergy. Someone with coeliac disease should communicate their diagnosis explicitly rather than describing it as a gluten intolerance.

Can someone with a nut allergy eat food from your kitchen safely?

Our kitchen is 100% nut-free — no nuts of any kind enter the building, which is a structural guarantee rather than a procedural precaution. For someone with a nut allergy, including those at anaphylaxis risk, this removes the cross-contamination risk at source. Every item also carries full Natasha's Law allergen labelling confirming the absence of nuts as an ingredient.

How do I know if I have a food allergy, a food intolerance, or coeliac disease?

Self-diagnosis from symptoms alone is unreliable for all three. Food allergy diagnosis requires clinical assessment including blood tests and potentially supervised food challenges. Coeliac disease requires a blood test and intestinal biopsy, and gluten must be eaten regularly until testing is complete. Food intolerance is typically diagnosed by exclusion after allergy and coeliac disease are ruled out. A GP referral is the right starting point for any of these.

If someone describes themselves as "gluten-free" when ordering catering, how should I clarify their needs?

Ask whether this is diagnosed coeliac disease, a wheat allergy, non-coeliac gluten sensitivity, or a personal preference. Each has different implications for how rigorously cross-contamination needs to be managed. Coeliac disease and wheat allergy require strict avoidance and honest information about kitchen practices; non-coeliac sensitivity and preference still deserve clear labelling and honest communication but may tolerate a different risk level.