Oral Allergy Syndrome



  • Allergic symptom confined primarily to the oral cavity caused by ingestion of fresh plant foods is known as oral allergy syndrome (OAS).
  • OAS: where sensitization to a plant-derived protein, typically found in pollen, elicits immediate oral symptoms to fresh plant foods (i.e., fruits, vegetables, legumes, and nuts) via mucosal mast cell recognition of their homologous protein structures
  • By definition, symptoms are isolated to the oropharynx and include itching of the mouth, lips, tongue, palate, throat, and ears. However, a minority of patients may also experience visible oral swelling, sensation of throat tightness, or systemic symptoms such as nausea, wheeze, or generalized urticaria. Rarely, anaphylaxis can occur.
  • Because of the lability of these shared structures, these foods can often be consumed without symptoms after being cooked.
  • OAS is often referred to pollen-food allergy syndrome or pollen-food syndrome.



  • Closely associated with the incidence of conditions associated with aeroallergy such as allergic rhinoconjunctivitis, allergic asthma, and atopic dermatitis. The incidence of all allergic conditions is increasing.
  • Because OAS occurs in the setting of sensitization to various pollens, the epidemiology varies regionally in accordance with local pollen exposures.

Studies suggest 23–76% of patients with pollen-induced allergic rhinitis have OAS. Of those patients with OAS, 8.7% experience systemic symptoms and anaphylaxis occurs in 1.7% (1).

Etiology and Pathophysiology

  • Homology exists between various pollen proteins and those in many fruits, vegetables, legumes, and tree nuts. Therefore, these food proteins are recognized by oral mucosal mast cells, thereby causing local mast cell degranulation and local release of histamine and other allergic mediators. Because most of these proteins are labile, they are rapidly denatured by digestive enzymes and heating. Therefore, consumption of the food in a cooked form typically causes no symptoms.
  • The most common cross reactors include:
    • Birch pollen (a spring pollen) with apple, stone fruits, almond, carrot, celery, soy, peanut, and hazelnut
    • Orchard grass (summer) with melon, peanut, white potato, and tomato
    • Ragweed (late summer/early fall) with melons and banana
    • Mugwort (late summer early fall) with celery, carrot, mustard, peach, parsley
  • Patients with mugwort allergy (late summer/fall) and symptoms with mustard, celery, carrot, or peach may have more severe manifestations of OAS and may be at increased risk for anaphylaxis.
  • Patients with OAS symptoms with legumes (including peanut) and tree nuts may be at an increased risk for anaphylaxis (1,2).
  • Natural rubber latex (a product of the Hevea brasiliensis tree) cross-reacts with the following: avocado, kiwi, banana, peach, tomato, fig, bell pepper.

Inheritability of allergic rhinitis is high, estimated to be 0.22 to 0.75 of the general population (2).

Risk Factors

  • Sensitization to pollen, which can manifest in the following conditions: allergic rhinitis, allergic conjunctivitis, atopic dermatitis, allergic asthma, eosinophilic esophagitis, or allergic contact dermatitis
  • Preexisting IgE-mediated food allergy
  • Sensitization to natural rubber latex, causing either allergic contact dermatitis, contact urticaria, or anaphylaxis

Commonly Associated Conditions

  • Seasonal and perennial allergic rhinitis (very common)
  • Allergic asthma (common)
  • Allergic contact dermatitis (common)
  • Atopic dermatitis (common)
  • Eosinophilic esophagitis (uncommon)

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