What Is “Oral Allergy Syndrome”?

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What Is “Oral Allergy Syndrome”?

If you have allergic rhinitis (hay fever), you may notice that your mouth or throat becomes itchy when eating certain foods, usually a fresh fruit or raw vegetable but it could also be a nut or spice.

This reaction occurs because proteins found in some foods are extremely similar to proteins found in the pollen of certain plants.  What is called cross-reactivity occurs.  Your body reacts to proteins in the specific fruit or vegetable, thinking it is the pollen protein.


In the case of allergic rhinitis and foods, this cross-reactivity has been labeled oral allergy syndrome (OAS), or pollen-food syndrome.

Let’s illustrate this with some specifics.

  • One of the best known oral allergy syndrome combinations is birch pollen with apples, almonds, carrots, celery, peaches, pears, plums, and raw potatoes.  So when someone with a birch pollen allergy eats an apple, they may notice an itchy mouth or other allergic reaction.
  • Another fairly common combination is ragweed pollen with bananas, cucumbers, melons (honey dew, cantaloupe, watermelon), tomatoes, and zucchinis.
  • Grass pollen can cross react with celery, oranges, peaches, and tomatoes.
  • The least known combination is mugwort pollen with apples, carrots, celery, peanuts and various spices.


What Can Happen??!!

Sore Throat

The allergic reaction can be highly variable.  The most frequent reaction involves itchiness or mild swelling of the mouth, face, lips, tongue, and throat.

The reaction usually occurs immediately upon eating the food, but can be seen up to an hour after eating, and it rarely progresses beyond the mouth/throat.  Once the food is swallowed (or spit out) the symptoms subside quickly.

Treatment is rarely necessary.  In less than 2% of patients* the reaction can be severe, with severe throat swelling that hampers breathing and a systemic reaction that includes a drop in blood pressure.  This is called an anaphylactic reaction and requires medical attention immediately.


Oral allergy syndrome can happen at any time of the year.  The pollen does not have to be out in order for you to experience the reaction to the food.

People who have the syndrome usually find that they can eat the cooked version of the fruit or vegetable because the proteins are changed with the heat of cooking.  They are no longer recognized by the immune system as a problem protein. The allergy usually shows up in older children, teens, and young adults who have been eating the foods in question without problems for many years.



No cure exists for oral allergy syndrome.  The best thing to do is avoid the foods you know you have allergic reactions too.

Do not assume that your allergic reaction, which may be mild right now, could not escalate to a more systemic reaction.  About 9 % of people have a more systemic reaction.

If you are worried that you reaction is fairly strong do not hesitate to consult with an allergy specialist who can prescribe an epi-pen to carry with you, just in case.  No matter how careful you are, sometimes a food will be in an item you didn’t expect to find it in and you will have a reaction.

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