Explaining Oral Allergy Syndrome

Explaining OAS

Some people get itchiness in their mouth or throat after eating certain fruits like melon or peaches. Many would think it is a food allergy to the fruit or vegetable and believe they need to stop eating that food. However, as with all food allergies, we encourage you to seek the advice of a board-certified allergist who can help determine the actual cause of these symptoms. In some cases, this itchy reaction could be caused by a condition called oral allergy syndrome.

What is Oral Allergy Syndrome?

According to the American College of Allergy, Asthma and Immunology, oral allergy syndrome (OAS) are “caused by cross-reacting allergens found in both pollen and raw fruits, vegetables, or some tree nuts.” It is also known as pollen-food allergy syndrome due to the connection between pollen and foods, and it is often developed by patients who have seasonal allergies. Some fruits and vegetables have a protein that the immune system may recognize similar to pollen that you are allergic to and then reacts to it. The itchiness in their mouth or throat is a reaction typically occurs shortly after eating the produce.

What are the symptoms of OAS?

It is important to know the difference between OAS and food-induced anaphylaxis. The main difference is that OAS symptoms are always limited to the lips, mouth, or throat and usually go away without treatment. Although specific proteins cause both types of allergic reactions, anaphylaxis is a much more severe form of food allergy and requires injectable epinephrine for treatment. Anaphylactic reactions may include generalized hives, swelling of the lips, eyelids, face, or hands; difficulty breathing; or loss of consciousness. Most food-induced anaphylactic reactions are due to foods such as peanuts, tree nuts, fish, shellfish, milk, or eggs. 

Which produce can cross-react?

The list below shows common pollens and their cross-reacting fruits or vegetables. Fortunately, just because you are allergic to birch, grass, or ragweed pollen doesn’t mean you will experience a cross-reaction with any of the foods listed. Also, even if you react to one of the foods, it does not necessarily mean you’ll react with all or any of the other foods. 

Birch PollenGrass PollenRagweed Pollen
Foods that may cross-react:Apple Almond Carrot Celery Cherry Hazelnut Kiwi Peach Pear PlumCelery Melon Orange Peach TomatoBanana, Cucumber Melon Sunflower seeds Zucchini

How is OAS diagnosed?

An allergist can make the diagnosis of OAS most often from a patient’s history. Skin testing with extracts of the suspected fruits and vegetables or blood testing for food-specific allergic antibodies may produce negative results in many cases. However, skin tests will be positive if fresh fruits or raw vegetables are used for testing.

What to do if you have OAS?

Once a patient knows what foods trigger a reaction, we recommend avoiding that food to manage the allergy. For OAS, peeling or cooking the food may allow patients to eat it, but we recommend avoiding eating the fresh food. The cooking process can destroy the proteins that cause the reaction, so if a patient experiences symptoms after eating an apple, they may still be able to eat applesauce or apple pie. Some studies have shown that treating the pollen allergy that correlates the foods with allergy shots can improve the symptoms.

Our doctors are here to help if you struggle with these symptoms and are concerned it could be a more severe reaction. Schedule an appointment with a board-certified allergist who can discuss management for any allergies you may have.