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When Pollen Meets Food Allergens: Pollen-Food Syndrome (PFS) - Part I

HK BioTek Intern

Springtime is undoubtedly a delightful season for those who enjoy flower-viewing, but it is also a headache for those who allergic to pollen.


Pollens may be chemically and structurally similar to certain plant food proteins. Hence, if a person has ingested a certain plant food protein, our body’s immune system may mistake the plant food protein for pollen, which may invade our body. This directs the body’s pollen-specific antibodies to cross-react with the plant food protein(s), which initiates an allergic reaction, or worsens existing hayfever (known as allergic rhinitis), a pollen allergy symptom.

The cross-reaction between pollen and corresponding plant food protein(s) produces mild food allergy symptoms collectively known as the pollen-food syndrome (PFS), which in fact is the most common type of food allergy among adults. Up to 90% of those with pollen allergy are allergic to foods that cross-react with pollen.


Types of PFS

The pollen and foods involved in the cross-reaction of PFS vary seasonally. Among which, the spring-exclusive PFS induced by the cross-reaction between airborne pollens of birch (or trees with tall, thin trunks and white bark), and raw, birch-related fruits and vegetables is most common. Birch-related foods involved in the common cross-reaction include Rosaceae fruits (e.g., apple, cherry, kiwi, peach, pear, plum), Apiaceae vegetables (e.g., carrot, celery, parsley, coriander), tree nuts (e.g., almonds, peanuts and hazelnuts), and even soybeans.


According to the American Academy of Allergy Asthma & Immunology (AAAI), 50 to 75% of adults are allergic to birch tree pollen, thus explains why pollen allergy and PFS symptoms usually exacerbate in March and/or April. Birch pollen may be the most common trigger for PFS, but experts suggest that people who are allergic to both birch and grass pollens are more likely to develop PFS than those who are allergic to birch pollen alone. Despite the claim, further research is required for validation.


Symptoms of PFS

PFS is an acute immune reaction mediated by the IgE antibody. A person with PFS usually experiences itching or tingling in the mouth and throat almost immediately after eating raw, birch-related fruits and vegetables. Some people may even get hives in areas where the food touches the skin, or experience swelling of the mouth, lips, tongue and throat after exposing to the allergens. Since the cross-reaction between pollen and food allergens occur mainly in the oral cavities, PFS is also called the oral allergy syndrome (OAS).


In other words, PFS symptoms normally do not progress beyond the mouth. Although a study has discovered that PFAS progressed to more serious symptoms in about 10% of patients, and although peaches and tree nuts may increase the risk of a systemic reactions, developing systematic symptoms or anaphylaxis, a fatal allergic reaction that sets in quickly after exposing to the allergen, is uncommon.


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