Oral Allergy Syndrome (OAS)

The itchy, watery eyes, or that sudden tingling, itching or burning sensation in your mouth is all too familiar: it must be ragweed season again!

After your soccer game, the juicy watermelon you share with a friend makes your mouth itchy, and you decide that maybe next time you will have to pass on the watermelon.

But this is strange: you knew you were allergic to ragweed, but your reaction to watermelon is brand new.

Although there is still so much we do not know about allergies, we do know that certain types of foods, or pollen like ragweed, are common culprits when it comes to giving the body an allergic reaction. Allergic reactions happen when a person’s immune system recognizes certain proteins called allergens, as foreign or unsafe. The body’s immune system then triggers an allergic response, like the swelling in your tongue and lips, to fight off the allergen.

Oral Allergy Syndrome Some allergies can be much more complex, even downright sneaky. Oral Allergy Syndrome (OAS) is one such allergy. Certain types of fruits, vegetables, and nuts can trigger OAS, but you can also develop OAS even if you were not previously allergic to any of these foods.

OAS only occurs in people who have pollen allergies. It is caused by allergens in fruit, vegetables and nuts that are very similar to allergens in pollen. Most only experience oral symptoms, but about 10% can experience nausea or stomach upset, and less than 5% will develop more serious whole-body allergic reactions, such as generalized hives, trouble breathing, or loss of consciousness.

You can react to something you were not previously allergic to because your immune system gets confused. The protein molecules that make up the watermelon were mistaken by your immune system for ragweed pollen allergens. Your immune system triggers the allergic response to fight off the protein molecules because it thinks they are the pollen allergens. Basically, your ragweed allergy and a confused immune system are the reasons you reacted to the watermelon.

If you have an allergy to birch, you can react to apples, carrots or even almonds. An allergy to ragweed can give you a reaction to melons, zucchini, cucumber and banana.

These are just a few examples of the fruits, vegetables or nuts that can be involved in OAS. If you think you might have OAS, speak to your allergist.

This information was adapted from www.aboutkidshealth.ca