GPAtlas🧭 When to suspect
Food allergy is an adverse immune response to a food. It is not the same as food intolerance, which is a non-immune reaction (for example lactose intolerance from enzyme deficiency) and is managed quite differently. The cardinal skill in primary care is to take a structured allergy-focused clinical history, decide which of two patterns fits, and then judge the risk of a severe reaction.
Suspect food allergy when symptoms occur reproducibly after eating a particular food – skin (urticaria, angioedema, itch), gut (vomiting, diarrhoea, reflux, colic), or airway/breathing (wheeze, throat tightness, breathlessness). The two mechanisms behave differently and this distinction drives the whole work-up. IgE stands for immunoglobulin E, the antibody that triggers immediate reactions.
| Feature | IgE-mediated | Non-IgE-mediated |
|---|---|---|
| Onset | Rapid – usually within minutes, almost always < 2 hours | Delayed – hours to days after ingestion |
| Typical features | Urticaria, angioedema, vomiting, wheeze, anaphylaxis | Reflux, loose or bloody stools, colic, eczema flare, faltering growth |
| Examples | Peanut, tree nut, egg, cow's milk, fish, shellfish reactions | Non-IgE cow's milk allergy, food protein-induced proctocolitis/enterocolitis |
| Helpful test | Specific IgE blood test or skin prick test (history-guided) | No validated blood test – trial elimination then reintroduction |
Raise suspicion particularly in those with a personal or family history of atopy (eczema, asthma, allergic rhinitis). Common triggers in children are cow's milk, egg, peanut, tree nuts, wheat, soya, fish, shellfish and sesame; in adults peanut, tree nuts, fish, shellfish and pollen-food syndrome predominate. Most childhood milk and egg allergy resolves with age, whereas peanut, tree nut and shellfish allergy tend to persist.
Source: NICE CG116 · BSACI
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🧠 Clinical pearl Pollen-food syndrome (PFS, also called oral allergy syndrome) is a common mimic. A pollen-sensitised patient – usually a hay-fever sufferer – gets immediate itching or tingling of the lips, mouth and throat after eating raw apple, stone fruit, kiwi, celery, carrot or nuts, but tolerates them cooked (the culprit proteins are heat-labile). It is usually mild and self-limiting. The trap is labelling it as a primary peanut or tree-nut anaphylaxis; if the history is classic for PFS, an adrenaline auto-injector is rarely needed, but atypical or systemic features warrant specialist testing. |
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