What are pollen-associated food reactions and which foods are commonly involved?

Pollen-Associated Food Reactions (Pollen-Food Allergy Syndrome)

Definition and Mechanism

Pollen-food allergy syndrome (PFAS), also known as oral allergy syndrome (OAS), is a hypersensitivity reaction to raw plant-based foods that occurs in individuals already sensitized to cross-reacting pollen allergens, manifesting primarily as itching of the lips, tongue, and mouth. 1 Unlike primary food allergy, PFAS requires prior sensitization to an inhalant pollen allergen rather than direct sensitization to the food protein itself. 2

The syndrome occurs when food proteins (pan-allergens) with high structural homology to pollen antigens are ingested, causing mast cells bound to pollen-specific IgE in the oral mucosa to cross-react with the food antigen, triggering a local type I allergic reaction. 3 The most common implicated proteins include PR-10 proteins (pathogenesis-related proteins family 10), profilins, and lipid transfer proteins. 4, 5

Clinical Presentation

Symptoms are typically limited to the oral cavity and pharynx, occurring within minutes of consuming raw plant foods. 1 However, a critical caveat is that PFAS can sometimes progress to or overlap with more severe systemic allergic reactions, including anaphylaxis. 1, 4

The typical presentation includes:

• Pruritus and tingling of the lips, tongue, palate, and throat 4, 2
• Local urticaria of the oropharyngeal mucous membranes 6
• Occasionally rhinitis, respiratory symptoms, skin manifestations, or anaphylactic shock 3

Specific Pollen-Food Associations

The foods involved depend on the specific pollen sensitization, with birch-apple being the prototype association. 4 The most clinically relevant pollen-food combinations include:

Birch Pollen Sensitization 1, 4

• Fruits: Apple, pear, plum, cherry, peach, apricot
• Vegetables: Celery, carrots
• Nuts: Hazelnuts, almonds

Grass Pollen Sensitization 3

• Various fruits and vegetables depending on geographic region
• Tomato, melon, watermelon

Ragweed Pollen Sensitization 3

• Melons (cantaloupe, honeydew, watermelon)
• Banana
• Cucumber, zucchini

Other Tree Pollens 1, 3

• Alder pollen: Similar cross-reactions to birch
• Various regional tree pollens with corresponding food associations

Important Clinical Distinctions

A crucial distinction must be made between PFAS and primary nut allergy, as this determines risk stratification and management. 6

• PFAS to nuts: Exclusive sensitization to PR-10 proteins and profilins indicates symptoms are due to PFAS, typically causing only local oral symptoms 6
• Primary nut allergy: Sensitization to seed storage proteins (with or without PR-10/profilin sensitization) indicates a more severe primary allergy phenotype with risk of systemic reactions 6

Effect of Food Processing

Cooked or processed forms of these foods are typically tolerated because the heat-labile proteins (especially PR-10) are destroyed during cooking. 1 This is a key distinguishing feature—patients with PFAS often tolerate:

• Baked goods containing the trigger food 1
• Cooked fruits and vegetables 1
• Canned or processed versions of the food 1

Diagnostic Approach

The allergist-immunologist should evaluate these reactions to determine the cause, advise which foods to avoid, identify other potential problematic foods, and assess risk for severe reactions. 1

Molecular allergology facilitates accurate diagnosis and risk stratification by establishing the specific sensitization profile. 5, 6 This approach:

• Identifies whether sensitization is to heat-labile proteins (PR-10, profilins) suggesting PFAS 5, 6
• Detects sensitization to more stable proteins (lipid transfer proteins, seed storage proteins) indicating higher risk of systemic reactions 5, 6
• Predicts cross-reactions with other foods containing homologous proteins 5

Standard testing includes skin prick tests and serum food-specific IgE, though these must be interpreted in clinical context. 1 In ambiguous cases, double-blind, placebo-controlled oral food challenges may be necessary. 4

Management Principles

Treatment primarily involves avoiding trigger foods in their raw form, with the extent of avoidance guided by the specific sensitization profile and reaction history. 4, 6

Key management points:

• Patients may tolerate cooked versions of the trigger food 1
• Epinephrine prescription is indicated when there is risk of systemic reactions, particularly with sensitization to lipid transfer proteins or seed storage proteins 5, 6
• Patients should be counseled that while most reactions remain localized, progression to systemic symptoms can occur 1, 4
• Seasonal variation in symptom severity may occur, correlating with pollen exposure 1

Prevalence and Epidemiology

The prevalence of PFAS varies by geographic region and predominant pollen type, affecting between 30% and 60% of individuals with food allergies. 4 PFAS typically manifests toward the end of the first decade of life in individuals with established pollen sensitization. 6