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). Furthermore, because most of the allergens are acid- and heat-labile, whatever food is swallowed is typically rapidly degraded by digestive enzymes and gastric acid. Most patients can tolerate the cooked or processed versions of the foods triggering symptoms.
OAS Is Not a 'Serious' Allergy: A Common Misperception
For all these reasons, OAS is often not considered a "serious" allergy—although there is some disagreement among allergists on how seriously to take this problem (reportedly, 30% never prescribe injectable epinephrine for possible anaphylaxis, whereas 3% always do).[2] Not only do some patients with OAS experience anaphylaxis after eating the putative food, others may develop an anaphylactic reaction only under certain circumstances.
It might seem obvious to us that a patient would avoid drinking a concentrated amount of a food that already triggers palatal pruritus, but this can easily happen. I recently blogged about how smoothies and other blended fruit and vegetable drinks may be ingested so quickly as to not trigger palatal pruritus as a warning symptom of possible anaphylaxis.
OAS may be thought of as a nuanced food allergy. Soy and almonds may cross-react with birch, and many patients tolerate processed soy, cooked tofu, and roasted almonds but not almond or soy milks, which some smoothies may contain.[3]
It is my habit, then, to always caution patients with OAS to be careful about the ingredients of blended beverages and to help them understand that cofactors can augment an allergic response. For example, a brisk walk on a warm day after drinking a blended fruit or vegetable beverage could stimulate an anaphylactic reaction, as I have seen this many times in practice.
It is also my contention that we will see more of this owing to a warming planet and anticipated higher pollen counts, higher seasonal allergen-specific immunoglobulin E levels, and more OAS—and hence a greater risk for this potential cause of anaphylaxis.
Medscape Allergy & Immunology © 2015 WebMD, LLC
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Gary Stadtmauer. Oral Allergy Syndrome: When an Apple a Day Is Not Advised - Medscape - Dec 10, 2015.
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