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The Fruit and Vegetable Section

Oral Allergy Syndrome: Why do Pollens and Foods Cross-React?

Cooking Out Trouble

Boiling, baking or microwaving almost every oral allergy offender – with the exception of celery and nuts – will usually break some of the bonds holding the protein in shape. When that three-dimensional structure is altered significantly, pollen-allergy antibodies aren’t nearly as likely to be drawn to it.

However, the inconsistent reactions to raw and cooked foods can cause confusion. “Patients sometimes think, ‘I can’t eat apples, but I can drink apple juice and have apple pie?’ So they figure it’s all in their head,” Ham Pong says.

Or they may conclude they’re reacting to pesticides sprayed on fruit, or wax, or pollen that has fallen on it. Sorry, says the expert; you’re allergic to that food.

Anaphylaxis, Alcohol, Big Dose Risks

An oral allergy reaction, even to peanut or a tree nut, does not usually escalate to anaphylaxis. However, 1 to 2 per cent of those with oral allergy syndrome are, in fact, susceptible to severe reactions.

With OAS, celery, kiwi, nuts (especially hazelnuts), peaches, apricots and apples are the most likely triggers of anaphylaxis, although Ham Pong notes that reactions to these foods are not always that dire.

Also, drinking alcohol, exercise, and consuming a large dose quickly, such as chugging down a bottle of raw carrot juice, can all increase the intensity of an oral allergy syndrome reaction.

Unfortunately, it may be difficult for an allergist to tell you if allergy symptoms are a cross-reaction to tree pollen, or if you’re reacting directly to the food.

Studies have found people with birch pollen allergies can have positive skin-prick and blood test results to apples, carrots, peanuts, and others, even if they don’t react when they eat those foods. Such false-positive tests make it hard for allergists to say for sure whether pollen or food is the allergy instigator. There are new protein “component” tests that your allergist may turn to in order to refine the analysis of your condition.

One final consideration: what would happen if someone with OAS munched on some leaves from a birch tree? Probably nothing, Ham Pong says, because the reaction-sparking proteins are localized in specific parts of the plant, like the fruit.

See Also:
Allergic Living‘s chart on OAS cross-reactors.

First published in Allergic Living magazine.
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