Peanut allergy

Where might peanut be found?

Which symptoms may occur?

Why can tests be positive to several legumes?

Legumes share certain protein families. IgE cross-reactivity may therefore occur between peanut, lupin, soy, peas, lentils, chickpeas, beans or broad beans. However, laboratory cross-reactivity does not mean that a clinical reaction to the food will occur systematically.

Peanut and lupin: an association to know

Lupin is used particularly as flour or protein in some bakery products, cakes and plant-based foods. True peanut-lupin cross-allergy is well documented and severe reactions are possible.

Peanut and soy

Peanut and soy are both legumes, and some of their proteins may be recognised by the same IgE. However, laboratory sensitisation to soy in a person with peanut allergy does not automatically mean clinical soy allergy.

What about other legumes?

What about tree nuts?

Peanut ≠ tree nut. People with peanut allergy may also have an independent allergy to one or more tree nuts, but this is not automatic. A tree nut that is already eaten regularly without a reaction should not be removed solely because peanut allergy has been diagnosed.

Peanut and birch pollen: Ara h 8

In some patients with birch pollen allergy, IgE directed against Bet v 1 recognises the related peanut protein Ara h 8. This may be associated with pollen-food allergy syndrome, mainly causing itching or tingling in the mouth and lips. This profile must be interpreted alongside the clinical history.

Step 1 — Medical history

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

• Legumes already tolerated.
• Tree nuts already tolerated.
• Any reactions to lupin or soy.
• Pollen allergy, particularly to birch.
• Asthma, previous reactions and any cofactors.

Step 2 — Skin prick tests and specific IgE

After taking a targeted clinical history, the allergist may offer skin prick tests and/or specific IgE testing. Their results are useful but must never be interpreted in isolation.

Step 3 — Molecular allergology

Step 4 — BAT in some centres

When the diagnosis remains uncertain despite skin prick tests and IgE testing, a basophil activation test (BAT) may be offered in some specialist centres where this technique is available.

Oral food challenge (OFC)

An oral food challenge (OFC) involves gradually giving the food under medical supervision. It may confirm or rule out an allergy, reassess an allergy over time or avoid unnecessary exclusion.

Why document the reaction precisely?

A photograph of the packaging, ingredients, date, amount, delay and symptoms may avoid unnecessary tests or help select the most relevant investigations. Also record any cofactors: exercise, alcohol, NSAIDs, infection or unusual circumstances.

What should be done when peanut allergy is confirmed?

• Targeted avoidance of peanut.
• Reading labels.
• A written action plan.
• Treatment of accidental reactions.
• An adrenaline auto-injector if indicated.
• Education for the patient and those around them.
• Dietetic support if needed.
• Continuing tolerated foods following medical advice.

Reading labels

In Europe, peanut, soy and lupin are among the allergens whose presence as an ingredient must be clearly declared. They are listed as three separate categories. Decisions about ‘may contain’ statements must be individualised with the allergy team.

Is oral immunotherapy a treatment option?

Peanut oral immunotherapy may be discussed for some children and adolescents in a specialist setting. Its main aim is to increase the reaction threshold and reduce risk from accidental exposure. It does not mean that the allergy has disappeared and does not replace emergency measures.

Common misconceptions

Before your appointment: the SOS Allergo checklist

• Packaging or a photograph of the product.
• Full ingredients, brand and product reference.
• Date and time of the reaction, amount eaten and delay before symptoms.
• Photographs of symptoms and the emergency department report.
• List of tolerated legumes and tree nuts.