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

How the immune system gets confused

Unfortunately for those with tree-pollen allergies, the pollen proteins that trigger hay fever symptoms are also found in a several foods.

The components of those proteins are well conserved among different plants, which means their three-dimensional structures are so similar that some of our immune systems can’t tell the difference between, say, birch pollen and apple peel.

In birch, the most common allergy troublemaker is a protein called Bet v 1, and alder has a similar protein called Aln g 1. Their purpose is to help protect the fruit or vegetable in times of stress or from infection.

Ham Pong explains that Bet v 1 is called a “pan-allergen” because very similar proteins are found in a variety of unrelated plants, including apples, plums, kiwis, carrots, celery, potatoes, hazelnuts, almonds, sunflower seeds, and even spices such as oregano, basil and dill.

People with birch-related oral allergy syndrome already produce antibodies to the pan-allergens from their prior exposure to birch pollen, so those antibodies will try to protect against similar proteins when they enter the mouth.

Pan-allergen relationships don’t stop with birch trees. The allergenic components of grass pollen are also shared with melons, oranges, kiwi, tomatoes and peanuts, among others.

Those who suffer in the fall from ragweed allergy (mainly in the northeast of the continent) can get itchy mouths from banana, melons, zucchini and cucumber.

For those reactive to ragweed, serious cross-reactions are also possible from consuming chamomile, honey and echinacea. This is not oral allergy syndrome, however. In this case, it’s because they belong to the same botanical family.

Next Page: The Trouble with Apples and Peaches