When it comes to allergies, rarely are they isolated or singular. Often there are groupings, like allergen punches in bunches, that can affect the body. Peanut allergy sufferers are often allergic to other types of tree nuts, or those allergic to ragweed pollen are also likely affected by dust mites. But more than being multi-allergenic, cross reactivity is also an issue for many allergy sufferers. Cross-reactivity is the body's immune system mistaking a similar protein or chemical as one it typically has a reaction to, and most people see this reaction with food.

So what are some common cross reactive allergens? Birch is one of the biggest culprits. A protein found in apple peels is very closely related to one found in birch, and this means the body can sometimes confuse the two. You may be diagnosed with an allergy to birch, but then, while eating a raw apple, you might experience tingling, swelling or itching around the mouth and lips. This type of symptom is most common for people with cross reactions to foods. Another example of this is with grass pollens and seemingly unrelated foods like kiwis, tomatoes, or peanuts. Sometimes referred to as "latex-fruit syndrome," a third common cross-reaction stems from a latex allergy and a sensitivity to certain fruits like bananas and kiwi.

Unfortunately, the problem with this can be felt year round. So while your spring allergy season may play hell on your birch pollen allergy, a reaction to eating fresh apples is likely to appear regardless of the season.

Challenges in identifying and categorizing these reactions can be difficult and cause false positive test results. Common allergen tests, like the skin prick test, can reveal a sensitivity to a particular allergen, potentially a cross reactive food, but then lead to a diagnosis of a full blown allergy to this food. Cross-reactivity does not mean that someone will have a reaction to ALL types of food that share a particular, similar protein. Because of this, eliminating an entire class of foods from the diet because of cross reactivity can sometimes be a bit unwarranted, though not uncommon.

One interesting away around this can be by cooking foods. While the cross reactions can be common when it comes to fresh food, cooked food often alters the proteins enough that the body no longer misidentifies them. This is not always the case (particularly with a cross-reaction to nuts), but this does explain why someone with a birch pollen allergy can feel a tingling in the lips and mouth when eating a fresh apple but experience no symptom at all when eating apple cobbler or drinking apple cider.

Without a doubt, cross reactivity complicates our understanding of allergies and the allergic response. Yet, solving the problem of allergies can't be solved until more is known, and cross reactivity is just another part of puzzle. If you think you may be cross-reactive, talk to your doctor or allergist. While the knowledge in this area is still rapidly expanding, he may be able to help further pinpoint the actual cause of the issue.

Author: K. Gilmore