Oral Allergy Syndrome (OAS)
(Pollen and Food Allergies)

By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
AAAC Collection Station—Birmingham, Alabama

Pollen and Allergic Reactions

Source: http://static5.businessinsider.com/image/59272dd7621e6c3d008b4d66-1201/fruit-vegetables-allergy-chart.png

Considerably more than 100 foods have been identified as causing food allergies, but there are a limited number of these that present a real public health concern. On a worldwide basis the foods of greatest concern are those causing serious allergic reactions. These foods are: gluten containing cereals, eggs, peanuts, milk, tree nuts, soybeans, fish, and crustacea. Food allergies result when foods having certain allergens (these are antigens that trigger an excessively vigorous immune response in which the immune system seeks to destroy a perceived threat that is actually harmless to the body) are contacted or consumed by allergen sensitive individuals.

Practically any object in the environment can act as an allergen: pollen, mold spores, feathers, house dust, drugs, pet dander, food, etc. This blog is concerned with those allergens in food that resemble allergens found on certain pollen grains that cause allergic reactions in sensitive individuals. Individuals who are sensitive to the pollen allergens develop allergic reactions when consuming, or even handling in some cases, foods having allergens that are similar to those found on pollen. Normally the foods are fruits, nuts, and vegetables that are consumed fresh (cooking usually destroys the allergens on the foods). This cross-reactivity between food and pollen allergens is referred to as oral allergy syndrome (OAS). OAS is observed only in people who have seasonal pollen allergies and most often these individuals are allergic to tree pollen. Up to 60% of the food allergies observed in adults result from cross-reactivity between foods and air-borne allergens found on pollen. Only foods that come from plants lead to OAS in susceptible individuals. OAS most commonly occurs during the season for the pollen that is similar to the food allergen that triggers an allergic reaction. However, OAS can occur at any time of the year. Symptoms can occur within minutes after ingesting food in individuals suffering from OAS, although symptoms may not develop for several hours after consumption of the triggering food(s).

Symptoms of OAS develop when the foods touch the mouth and throat. The most frequent symptoms involve itchiness or swelling of the mouth, face, lips, tongue, or throat. The allergens, which are proteins, are destroyed by stomach acid and thus the allergic reaction typically ceases once the food is swallowed. This is why OAS rarely leads to severe or life-threatening reactions. A number of foods that are associated with a particular pollen may trigger OAS, but normally only a small number of these foods will trigger an allergic reaction in any single individual. For example, if you are allergic to birch pollen then the following plants might trigger OAS in you; peach, pear, apple, cherry, plum, kiwi, coriander, fennel, parsley, celery, and carrot, but it is most likely than one or a few will trigger an event but not all of these plants.

Note: If you have a birch allergy, then you may find that you will develop mouth itching even when consuming peanuts, almonds, and hazelnuts. If you have mild mouth symptoms when consuming nuts, it is advisable to see an allergist because mild mouth symptoms may indicate a more serious allergic reaction to nuts is possible.

There is no definitive test available for determining if you are likely to experience OAS. Individuals affected by OAS will often have a positive allergy skin test or blood test for a specific pollen and have a history of experiencing allergic symptoms following ingestion of suspected foods.

A table listing pollens and plants that are associated with them that lead to OAS is shown below. The source of this table is the URL shown below the table. For additional tables and charts showing listings of pollens and plants associated with OAS check this resource.

This blog is not intended nor recommended as a substitute for medical advice or diagnosis from a qualified health care professional. Contact your own physician or qualified allergist if you have questions regarding oral allergy syndrome.