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Oral allergy syndrome: why raw apple itches in May

In birch country the commonest food reaction in adults is not a food allergy that started with food. It starts with pollen, and the food is collateral damage.

This is reference information, not a diagnosis and not a treatment plan. A pollen calendar cannot tell you what you are allergic to, and no page can clear a food as safe for you — only the label on the packet in your hand and the clinician who knows your history can do that. Anything beyond mild, short-lived symptoms in the mouth or nose — swelling that affects breathing or swallowing, hives away from the mouth, wheeze, vomiting or faintness — is an emergency question, not a reading question.

What is actually happening

Pollen-food allergy syndrome — usually shortened to oral allergy syndrome — is a cross-reaction. The immune system learns to recognise a protein in pollen, and then meets a near-identical protein in a raw plant food. The antibodies cannot tell them apart, so the food triggers a reaction in the mouth and throat where it first makes contact.

The proteins responsible are a small number of families that turn up throughout the plant kingdom. PR-10 proteins, the family that includes birch Bet v 1, apple Mal d 1 and soy Gly m 4, are the important ones in Northern Europe. Profilins, such as birch Bet v 2 and timothy Phl p 12, are a second family that produces broad, often symptomless, positive test results.

This is why the reaction follows the pollen calendar rather than the food. It is often worse during and just after the relevant pollen season, when the immune system is already primed, and it can be mild or absent in midwinter.

What it feels like

The classic picture is immediate and local: itching or tingling of the lips, tongue, palate and throat within minutes of a raw fruit, sometimes with slight swelling of the lips, and it settles within an hour without treatment. Many people describe it for years as "that apple was sour" before recognising the pattern.

Because the proteins are fragile, they are usually destroyed by stomach acid before they can be absorbed, which is why the reaction generally stops at the mouth. That is the reassuring part of the mechanism — and it is also exactly why the exceptions below matter.

Which pollen goes with which foods

The birch group — birch, alder, hazel and oak — carries the largest food list in this region: apple, pear, cherry, plum, peach, apricot, hazelnut, almond, carrot, celery, parsnip, kiwi, soy drink and peanut.

Mugwort carries celery and celeriac, carrot, and the carrot-family spices: parsley, caraway, coriander, cumin, fennel, aniseed and dill, plus black pepper, sunflower seed and chamomile.

Ragweed, which reaches this region mostly as transported pollen in late summer, carries the melon family: melon, watermelon, cucumber and courgette, plus banana.

Grass carries a shorter and weaker list: tomato, melon, orange and raw potato.

Why cooking usually fixes it

PR-10 proteins unfold when heated. That is why a raw apple causes an itchy mouth in May and an apple pie made from the same apples does not, why cooked carrot is generally fine when raw carrot is not, and why pasteurised apple juice behaves differently from fresh.

The same fragility applies to processing. Peeling helps with some fruits because the protein is concentrated near the skin, and varieties differ — this is well described for apples, where some cultivars are consistently better tolerated than others.

The exceptions that matter

Not every food reaction in a pollen-allergic person is harmless, and three exceptions deserve naming. Celery reactions through the mugwort route involve more heat-resistant proteins, and cooked celeriac and dried celery in spice mixes have caused systemic reactions. Nuts carry both a fragile pollen-related protein and heat-stable storage proteins, and only a test can say which one a given person has. And soy drink can deliver a large dose of Gly m 4 quickly, which has caused reactions beyond the mouth in birch-allergic adults.

A separate condition looks similar and is not: lipid transfer protein allergy, common in southern Europe and centred on peach, involves heat-stable and digestion-resistant proteins and causes systemic reactions. Someone from this region who reacts to peach abroad in a way they never do at home should have that looked at properly.

When to stop self-managing

Symptoms that stay in the mouth, settle quickly and only happen with raw plant foods are the ordinary picture. Anything beyond that — hives away from the mouth, swelling of the tongue or throat that affects breathing or swallowing, vomiting, wheeze, dizziness or a reaction to a cooked version of the food — is a different problem and needs assessment.

Component-resolved blood testing can distinguish a pollen-related protein from a storage protein, and that distinction changes whether a person needs an adrenaline autoinjector. It is worth asking for by name when a nut or a legume is involved.

The pollen groups at a glance

Sources: Regulation (EU) No 1169/2011, Annex II · Commission Implementing Regulation (EU) No 828/2014 (gluten claims) · WHO/IUIS Allergen Nomenclature · season windows from the national aerobiology monitoring programmes of Estonia, Finland, Sweden, Denmark and Norway · cross-reaction patterns paraphrased from the allergy literature and EAACI material · checked 2026-09-06

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