Tree nut allergy

Which tree nuts should be specified?

What symptoms may occur?

A precise record of the reaction

After a reaction, try to keep or record as much information as possible:

• Date and time of the reaction.
• Exact food or dish, brand and product name.
• Photo of the packaging and full ingredients list.
• Any ‘may contain’ statement.
• Recipe for home-made food or information from the restaurant.
• Identified tree nut or mixture; approximate amount.
• Raw, roasted, cooked, ground, paste or drink.
• Delay between eating and the first symptoms.
• Symptoms observed and photos if possible.
• Medicines given, any adrenaline, and emergency-department attendance.

Is a reaction limited to the mouth the same thing?

In someone allergic to birch pollen, antibodies directed against Bet v 1 may recognise similar proteins in certain foods, including Cor a 1 in hazelnut. This may cause pollen-food allergy syndrome, often involving itching or tingling of the lips, mouth or throat, particularly with the raw food.

This differs from primary hazelnut allergy directed against certain storage proteins such as Cor a 9 or Cor a 14, which are more associated with systemic reactions. Molecular tests help explain the profile but can never, on their own, predict exactly how severe a future reaction will be.

Which cross-allergies should be known?

What you eat without a problem also matters

Saying ‘I regularly eat almonds and hazelnuts without any problem’ is valuable information. A confirmed cashew-nut allergy does not mean that every other tree nut already eaten without a reaction must automatically be removed.

Step 1 — The history

The allergist reconstructs: food → amount → delay → symptoms → treatment → outcome.

• Tree nuts already tolerated.
• Peanut and, where relevant, sesame.
• Pollen allergy, particularly birch.
• Previous reactions and asthma.
• Possible cofactors.

Step 2 — Skin prick tests

These may be performed using allergen extracts and, depending on the situation and centre's practice, with the food itself. A positive test indicates sensitisation and must always be interpreted alongside the clinical history.

Step 3 — Specific IgE

Testing is targeted at the tree nut or nuts actually suspected. A large panel that ignores the history may identify sensitisation without clinical significance and needlessly complicate the diagnosis.

What about molecular IgE tests?

Oral food challenge (OFC)

An OFC is performed under medical supervision with gradually increasing doses. It may be used to confirm or exclude an allergy when assessment remains uncertain, check that a tree nut is genuinely tolerated, avoid unnecessary avoidance or reassess an allergy over time.

Why not avoid everything as a precaution?

Modern strategies seek to individualise avoidance. The aim is to make genuinely risky foods safe while avoiding unjustified dietary restrictions, particularly in children.

What happens when an allergy is confirmed?

• Avoid the responsible tree nut.
• Dietary advice and label reading.
• A written action plan.
• Treatment of accidental reactions.
• An adrenaline auto-injector when indicated.
• Education for the patient and those around them.
• Dietetic advice when several foods are avoided, especially in children.

Reading a label

In Europe, regulated tree nuts must be clearly declared when used as ingredients. Peanut is declared separately.

How to manage ‘trace’ statements should be individualised with the allergist rather than turned into a universal rule.

Common misconceptions

Before your appointment: the SOS Allergo checklist

• Packaging or a photo of the product.
• Ingredients list.
• Brand and product reference.
• Date and time of the reaction.
• Amount eaten.
• Delay before symptoms.
• Photos of hives or swelling.
• Tree nuts eaten without a problem.