What Exactly is Cross-Reactivity?

Lobster and dust mites. Latex and avocado. Carrots and mugwort.

What do each of these duos have in common? It might sound like the intro to a bad joke, but there’s actually a scientific explanation for these pairings: cross-reactivity.

In summary, cross-reactivity is when someone experiences an allergic response to a substance that shares similar proteins to another substance, resulting in some relatively unusual duos. For example, someone with a latex allergy may be unable to eat avocado simply because the two share similar proteins.

“The concept of cross-reactivity is that certain foods appear as offending substances to our immune system simply because they share a similar chemical structure,” says Dr. Chris Meletis, N.D. and Notch medical advisor.

It’s also important to note that there are different types of cross-reactivity. While cross-reactivity can occur between airborne allergens and food allergens, it can also occur between food groups as well. For example, people with a cow’s milk allergy may experience cross-reactions to veal or goat’s milk and those with a salmon allergy may experience reactions to other fish as well. This is particularly common in food groups such as tree nuts, seafood and grains.

What are some seasonal cross-reactants to be wary of?

Like most allergies, your reactions can be wholly dependent on the time of year. For example, with birch pollen and apples being one of the most common cross-reactant pairings, your reactivity will likely shift during birch season. This means that while you might enjoy eating certain foods eight months out of the year without any symptoms, January through May could result in an increased sensitivity to produce such as apples, carrots and celery.

In the late summer to early fall months, other allergens such as mugwort and ragweed might pose a threat to your diet, as they have many cross-reactants as well. This includes foods such as cantaloupe, cucumbers, bananas, bell peppers, onions, broccoli and more.

"If all of a sudden the foods you were eating are making you miserable, it could be the result of pollen and certain foods cross-reacting and triggering your immune system,” Meletis says.

Is cross-reactivity that same thing as cross-contact?

In short, no. Cross-reactivity is when different allergens have a similar molecular makeup, resulting in a reaction to both allergens, while cross-contact (or cross-contamination) is when an allergen is exposed to another allergen that it shouldn’t be exposed to. For example, on food labels you might read something along the lines of “processed in a facility that also processes wheat and soy.” This disclosure is letting you know about possible cross-contact in case you’re sensitive to either of the ingredients listed.

How do I know if I have cross-reactive allergies?

Like with food sensitivities, it can be hard to pinpoint specific allergens that may be linked to each other. However, if you already know of one allergy, you’ve got a head start. All you need to do is research common cross-reactive allergens and monitor for symptoms.

“If your body is talking to you, listen,” says Meletis. Simple precautions such as keeping your windows closed, staying hydrated, using a HEPA filter and washing your face before bed are just a few ways to reduce the possibility of experiencing cross-reactive symptoms, he says.

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