Recently, a friend asked why her cousin with pollen allergy was unable to eat raw apples as they cause itching and swelling of her throat. She can eat cooked apples, however, without symptoms.
This condition, usually known as pollen food allergy syndrome (PFAS) or alternatively oral-allergy syndrome (OAS) can occur in up to 50% of patients with pollen allergies.
OAS is caused by reaction to plant proteins cross-reacting with airborne pollen allergens. Symptoms are confined to oropharynx-include mouth burning/itching and minor swelling of lips, tongue, palate or throat upon ingestion of fresh fruits, vegetables or tree nuts.
Best example of PFAS is that of cross reactivity with birch pollen allergy with oral allergy symptoms occurring while eating raw apples, celery, carrots, pecans, potatoes and hazelnuts.
Oral allergy syndrome have also been reported with ingestion of: peaches, avocado, kiwi, apricot, cherry, plum and mango. Ragweed allergic patients may have OAS following the ingestion of fresh melons (watermelon, cantelope or honeydew) and bananas. Symptoms may be worse in ragweed season.
Diagnosis of OAS is usually by history and demonstration of sensitivity to pollen allergens especially birch tree pollen or ragweed. To demonstrate allergy to the food, a fresh extract from raw fruit or vegetables are made to be used for skin testing.
Clinically, the allergies in foods causing PFA are heat labile so patients with OAS can tolerate the food cooked (or canned). In addition, the allergens are quickly degraded by enzymes in saliva and by gastric acid , so symptoms are confined to the oral mucosa and do not normally cause anaphylaxis, hives or a drop in blood pressure.
Some patients on allergy injections or sublingual treatment to birch pollen have reported improvement in tolerance to raw apples (personal clinical observation at Allergycare of Chattanooga).
Summary: If you experience any symptoms of OAS, you should consider evaluation to document the pollen allergies. This should include skin testing as well as additional blood tests for food allergies (especially nuts and peanut). Not all symptoms are due to OAS and may instead be associated with severe food allergies capable of producing anaphylaxis-which could be life threatening..