Cross-allergy — why birch pollen is linked to apple

If you get hay fever from birch pollen in spring and feel itching of the mouth and throat after biting into a raw apple — it is no coincidence. This is the most common example of cross-allergy, also called oral allergy syndrome (OAS). In this article we explain factually where it comes from and what to do about it.

Important: this is an educational article. It does not replace a consultation with a doctor or allergy diagnostics. The indicative bioresonance tests offered at the AGAMED practice are support for well-being, not a diagnostic examination in the medical sense. In case of a severe reaction (swelling of the throat, shortness of breath), call for help immediately.

In brief

• Cross-allergy (oral allergy syndrome, also oral allergy syndrome / pollen-food syndrome) is a reaction in which the immune system confuses similar proteins in pollen and in plant foods.
• The flagship example: birch pollen (the protein Bet v 1) and raw apple (Mal d 1). Over 70% of people allergic to birch react.
• Symptoms are usually mild and short: tingling, itching of the lips, mouth and throat — they pass within a few minutes.
• Cooking usually removes the reaction — a baked apple or apple purée is most often well tolerated.
• Rarely, reactions can be stronger — in that case urgent medical help is needed.

What is cross-allergy?

Cross-allergy occurs when the immune system recognises a protein in a raw fruit, vegetable or nut as similar to the protein of a pollen you are allergic to. The body "confuses" one with the other and triggers a local reaction in the mouth.

That is why OAS mainly affects people with an inhalant allergy to pollen — and symptoms appear when eating specific raw foods.

Birch and apple — the most common pair

The main allergen of the apple, Mal d 1, is structurally very similar to the main allergen of birch pollen, Bet v 1. When a person allergic to birch eats a raw apple, their immune system recognises Mal d 1 as Bet v 1 and triggers a reaction in the mouth and throat. Studies indicate that this cross-reactivity affects over 70% of people with birch pollen allergy.

What else does birch cross-react with?

Besides apple, birch pollen cross-reacts, among others, with other fruits of the rose family (Rosaceae) — pear, peach, cherry, plum — as well as with hazelnut, carrot and celery. The set of "triggers" is slightly different for each person.

Why don't cooked fruits cause a reaction?

The proteins responsible for OAS (such as Mal d 1) are sensitive to temperature. During cooking or baking they break down (denature), so they are no longer recognised by the immune system. That is why apple purée or a baked apple usually does not cause symptoms, whereas a raw apple does.

When to stay alert

In most people OAS is mild and limited to the mouth. However, in some people reactions can be stronger. If swelling of the throat, difficulty swallowing or breathing appears — this is an urgent situation requiring immediate medical help. It is worth discussing the topic with an allergist, especially if symptoms are getting worse.

How to check it?

Recognising an allergy and its cross-links is the task of allergy diagnostics (interview, skin tests, IgE measurements, including molecular diagnostics). At the AGAMED practice in Szczecin we offer indicative bioresonance tests — as support and a starting point for a conversation, not a substitute for tests with an allergist. See: tests and desensitisation.

How we approach desensitisation of cross-allergies

Since the proteins of pollen and food are similar, does desensitising pollen also "take care of" the apple? We do not assume this in advance. At our practice we first desensitise the primary allergen (pollen) — according to the protocol, one allergen per session — and after 2–3 weeks, at a free follow-up, we check the cross-reacting foods again and desensitise only those that still react. Why exactly this way, and what to ask at any practice, we explain in the post Why we desensitise one allergen per session.

Frequently asked questions

Is cross-allergy dangerous?

It is usually mild and short-lived (itching of the mouth and throat). Rarely it is stronger — with swelling of the throat or shortness of breath, immediate medical help is needed.

Do I have to give up fruit?

Not always. Eating fruit after heat treatment (cooked, baked) often helps. Determine the extent of your tolerance individually, preferably with a doctor.

How do I know what exactly I react to?

This is determined by allergy diagnostics. Our bioresonance tests are indicative and auxiliary — they do not replace tests with an allergist.

Do you have allergy symptoms in Szczecin?

At the AGAMED practice in Szczecin we perform indicative bioresonance tests and supportive desensitisation. Tests and desensitisation · contact · tel. 519 055 858.

The information in this article is educational and is not medical advice.