Hazelnut allergy: a multi-faced condition with demographic and geographic characteristics.

Hazelnut (Corylus avellana) allergy varies from rather mild oral allergy symptoms to potentially life-threatening anaphylaxis and exhibits geographic and age-related variations. Severity of symptoms depends on the sensitisation profile of the patient and can partially be predicted using 'component-resolved diagnosis'. In our region (young) children predominantly exhibit sensitisation to hazelnut storage proteins Cor a 9 and Cor a 11 that is unrelated to birch pollen allergy and is generally associated with a more severe clinical outcome on consumption on raw and processed hazelnut. In contrast, adults predominantly present with an oral allergy syndrome due to an extensive cross-reactivity between the labile Cor a 1.04 and Bet v 1, the major allergen from birch (Betula verrucosa) pollen. In the absence of a cure, avoidance remains the key measure of effective management, particularly in those patients presenting with a severe form.