People who are allergic to birch pollen may also be hypersensitive to several foods, including apples, strawberries, celery, carrots, pulses, hazelnuts and soybeans, and there have been reports of particularly severe cross-allergic reactions after the consumption of peanuts.

Even when not directly exposed to birch pollen, a sufferer may experience a reaction after eating any of these foods because certain proteins in them are so similar in structure to the protein in birch pollen.

The trigger for the cross-reaction to soya products is the protein Gly m 4, which is similar in structure to the birch pollen allergen Bet v 1.

Typical symptoms of an allergic reaction to the Gly m 4 protein are itching and swelling of the mucous membranes in the mouth and throat, directly after eating soya products. Skin rashes or gastro-intestinal symptoms may also follow.

Highly sensitised individuals may experience severe allergic reactions and, in some cases, even anaphylactic shock is possible, coupled with serious circulatory disorders.

As the activity of the soya protein Gly m 4 can be reduced or destroyed by heating to high temperatures, it may be safe to eat products with soya ingredients if they have been heated during processing.

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First published in July 2008

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