Pollen food allergy syndrome

Oral allergy syndrome (OAS) or pollen-food allergy syndrome (PFAS) is a type of food allergy classified by a cluster of allergic reactions in the mouth and throat in response to eating certain fruits, nuts, and vegetables that typically develops in adults with hay fever.

PFAS occurs in individuals that have been sensitized aerosolized environmental plant pollens via the respiratory tract, who then ingest plant-based foods that cross link the pollen specific IgE.

OAS is not a separate food allergy, but rather represents cross-reactivity between distant remnants of tree or weed pollen still found in certain fruits and vegetables. 

OAS is only seen in people with seasonal pollen allergies, and mostly people who are allergic to tree pollen.

It is usually limited to ingestion of uncooked fruits or vegetables.

In adults, up to 60% of all food allergic reactions are due to cross-reactions between foods and inhalative allergens.

It is a Type 1 or immunoglobulin E-mediated hypersensitivity.

The body’s immune system produces IgE antibodies against pollen; in PFAS, these antibodies also bind to, or cross-react with, other structurally similar proteins found in botanically related plants.

PFAS can occur any time of the year, but is most prevalent during the pollen season. 

Patients usually develop symptoms within minutes of eating the food.

The most common reaction is an itching or burning sensation in the lips, mouth, ear canal, or pharynx. 

Adverse reactions are typically limited to immediate local, oral phrenitis and angioedema.

Other reactions can be triggered in the eyes, nose, and skin, with swelling of the lips, tongue, and uvula, and a sensation of tightness in the throat.

When the food allergen reaches the stomach, it is broken down by the acid, and the allergic reaction does not progress.

If the allergen is not destroyed by the stomach acids, it is likely that there will be a reaction from histamine release later in the gastrointestinal tract, and vomiting, diarrhea, severe indigestion, or cramps may occur.

PFAS may be severe and present as wheezing, vomiting, hives, low blood pressure, or anaphylaxis.  

Anaphylaxis has been reported in 1.7% of patients with PFAS.

An allergic person can be sensitized to allergenic pollen proteins through the respiratory route and develop an allergy to heat labile food proteins in certain fruits and vegetables, which cross-react with pollen proteins.

PFAS symptoms occur when an affected person eats certain fruits, vegetables, and nuts. 

Patients may show allergy to one or many foods.

Individuals with an allergy to tree pollen may develop allergy to a variety of foods. 

Some individuals have severe reactions to certain fruits and vegetables that do not fall into any particular allergy category. 

Because the allergenic proteins associated with OAS are usually destroyed by cooking, most reactions are caused by eating raw foods.

Celery and nuts may cause reactions even after being cooked.

Allergies to a specific pollen are usually associated with oral allergy reactions to other certain foods: allergy to ragweed is associated with reactions to banana, watermelon, cantaloupe, honeydew, zucchini, and cucumber. 

Alder pollen: almonds, apples, celery, cherries, hazel nuts, peaches, pears, parsley, raspberry, strawberry.

Birch pollen: apples, peach, pear, cherry.carrots, celery, , chicory,coriander, fennel, fig, hazel nuts, kiwifruit, nectarines, parsley, parsnips, peaches, pears, peppers, plums, potatoes, prunes, soy, strawberries, wheat, jackfruit; Potential: walnuts

Grass pollen: melons, tomatoes, oranges, celery, peach

Mugwort pollen: carrots, celery, and mustard.

Ragweed pollen: banana and melons, honeydew, watermelon,cantaloupe, cucumber, green pepper, paprika, sunflower seeds/oil, zucchini, echinacea, artichoke, dandelions, honey

20 to 43% of children and adults with the allergic rhinitis in Asia and Europe report PFAS symptoms.


History of atopy and an atopic family history common.

Eczema, otolaryngeal symptoms of hay fever or asthma will often dominate.

Well-cooked, canned, pasteurized, or frozen food cause little to no reaction due to denaturation of the cross-reacting proteins, and cause a  delay and confusion in diagnosis.

Oral reactions to food are often mistakenly self-diagnosed by patients as caused by pesticides or other contaminants, and  reactions to food, such as lactose intolerance and intolerances which result from a patient being unable to metabolize naturally occurring chemicals such as salicylates and proteins in food must be distinguished from the systemic symptoms PFAS.

The diagnosis of OAS may involve skin prick tests, blood tests, patch tests or oral challenges.


OAS must be managed in conjunction with the patient’s other allergies, primarily the allergy to pollen. 

Symptoms may wax and wane with the pollen levels. 

Patients are advised to avoid the triggering foods, particularly nuts. 

Peeling or cooking the foods has been shown to eliminate the effects of some allergens such as apple, but not others such as celery or strawberry. 

Antihistamines may also relieve the symptoms of the allergy by blocking the immune pathway.

Oral steroids may also be helpful. 

Allergy immunotherapy has been reported to improve or cure OAS in some patients.

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