One little girl with severe ragweed allergy used to complain to her father that eating melon, banana, cucumber and tomato made her throat and inner ears itch. He thought it was just her imagination. However, it is now recognized that symptoms such as these are caused by a type of food-related allergic reaction called Oral Allergy Syndrome (OAS). Adults and children who are allergic to inhaled pollens (tree, grass and ragweed pollens) and who usually have seasonal allergic rhinitis (hay fever) may experience symptoms after eating certain raw vegetables, nuts, seeds, or fresh fruit.
Food and Pollen Cross-Reactions
OAS is caused by nearly identical allergens that are present in both fresh food and pollens, called cross-reacting allergens. The foods that are most commonly associated with OAS are listed in the accompanying table. The symptoms of OAS occur where the food touches the mouth, which results in itching or swelling of the lips, tongue, back of the throat, or roof of the mouth.
Because the allergens that are responsible for these symptoms are usually destroyed by heat from cooking procedures, affected individuals can usually eat fruits or vegetables that have been cooked, baked, or canned. For example, a person may experience itching of the tongue and roof of the mouth when eating a fresh apple, but have no problems after consuming apple pie or apple sauce.
Specific cross-reactions have been identified between ragweed pollen and watermelon, other melons, and members of the gourd family including cucumber and squash. Cross-reactions between birch pollen and celery, kiwi, apples, and hazelnuts have also been found. See the accompanying table for other fresh fruit and vegetable allergen cross-reactivities with grass, tree and ragweed pollens.
Diagnosis and Treatment
Allergists can make the diagnosis of OAS most often from a complete clinical history. If skin testing with commercial extracts of the incriminated fruits and vegetables or blood testing for food-specific IgE (allergic) antibodies produces negative results, skin tests done with fresh fruits or raw vegetables will usually be positive. Skin testing to the cross-reacting pollens will also be positive.
The natural history of patients with OAS has not been well studied. Some researchers report that both allergic rhinitis (hay fever) symptoms and OAS symptoms go away if the affected individual receives immunotherapy injections with extracts of the cross-reacting pollens. Patients with OAS also report that some improvement occurs with the use of regular doses of antihistamines.
However, this form of treatment is not advised in patients with any history of systemic (affecting the entire body) reactions to foods. In patients who experience not only oral symptoms but serious systemic reactions to foods, identifying the responsible food and strictly avoiding that food is the key to successful long-term management.
While Oral Allergy Syndrome is not a typical food allergy, it is a food-related allergic reaction. It may improve with treatment of the allergic rhinitis, but patients with persistent bothersome symptoms should avoid raw forms of the offending foods, especially during the pollen season.