OAS: An Introduction
Whoever said "an apple a day keeps the doctor away" clearly did not know anyone with oral allergy syndrome (OAS), also known as "pollen-fruit allergy syndrome." In this condition, immunoglobulin E-mediated hypersensitivity to an environmental allergen triggers food allergy.[1]
The most commonly cited example is that of birch pollen-sensitive patients with allergic rhinitis or conjunctivitis, who become sensitive to raw fruits, vegetables, soy, and some nuts (Table). Although this is extremely common, serious reactions are rare—but, in my opinion, many of these patients have the potential for anaphylaxis and should be warned appropriately.
Table. Corresponding Food and Airborne Allergens
| Airborne allergen | Food |
|---|---|
| Birch pollen | Carrots |
| Celery | |
| Fresh fruit (eg, apples, cherries, nectarines, peaches, pears) | |
| Hazelnuts | |
| Parsnips | |
| Potatoes | |
| Soy | |
| Almond | |
| Grass pollen | Kiwi |
| Tomatoes | |
| Ragweed pollen | Bananas |
| Melons (eg, cantaloupe, honeydew, watermelon) | |
| Latex | Bananas |
| Avocado | |
| Kiwi | |
| Chestnuts | |
| Others occasionally, including tomato, eggplant, melons |
Patients with this "mild food allergy" are described as having symptoms limited to the oropharynx (hence the term "oral allergy syndrome"). This type of allergic reaction is self-limited because the immediate discomfort of oral histamine release causes most patients to stop eating (patients may report tightness in the throat, but this may be attributed to posterior pharyngeal as opposed to laryngeal edema).
