What are the clinical manifestations of Oral Allergy Syndrome (OAS)?

From the Guidelines

Oral allergy syndrome (OAS) typically manifests as immediate allergic symptoms, including itching, tingling, and swelling of the lips, tongue, palate, and throat, which usually begin within minutes of eating the triggering food. The primary clinical manifestations of OAS include:

• Itching, tingling, and swelling of the lips, tongue, palate, and throat
• Itchy ears
• Tightness in the throat
• Mild swelling of the uvula These symptoms are generally confined to the oral cavity and oropharynx, and typically resolve quickly once the food is swallowed or removed from the mouth 1. In rare cases, OAS can progress to more severe systemic reactions, including nausea, vomiting, abdominal pain, rhinoconjunctivitis, or even anaphylaxis. The syndrome occurs because of cross-reactivity between proteins in certain pollens and structurally similar proteins found in raw plant foods. According to the guidelines for the diagnosis and management of food allergy in the United States, milder forms of allergic reactions, such as flushing, urticaria, isolated mild angioedema, or symptoms of OAS, can be treated with H1 and H2 antihistamine medications 1.

Management of OAS includes avoiding raw trigger foods, cooking or processing foods before consumption, and having antihistamines available for mild reactions. Patients with more severe reactions should carry epinephrine auto-injectors and consider formal allergy testing to identify specific triggers. It is crucial to monitor patients with OAS for signs of progression to more severe symptoms, and epinephrine should be administered immediately if progression or increased severity is noted 1.

From the Research

Clinical Manifestations of Oral Allergy Syndrome

The clinical manifestations of oral allergy syndrome (OAS) are characterized by mild transient oropharyngeal symptoms, including:

• Pruritus of the lips, tongue, and mouth 2
• Mouth and throat itching, which starts rapidly after a food is placed in the mouth 3
• Symptoms that typically continue for just a couple of minutes after the food has been swallowed 3

Systemic and Anaphylactic Reactions

While OAS is usually associated with mild symptoms, some individuals may experience systemic and anaphylactic reactions, including:

• Systemic symptoms outside the gastrointestinal tract in 8.7% of patients 4
• Anaphylactic shock in 1.7% of patients 4
• Extreme responses, such as anaphylaxis, in 1-2% of patients with OAS and pollen allergy 3

Triggers and Cross-Reactivities

OAS is often triggered by cross-reactive aeroallergen sensitization, including:

• Birch tree pollen, ragweed pollen, and grass pollen hypersensitivity 3
• Cross-reactivities between allergens, such as heat-labile PR-10 protein, partially labile profilin, and relatively heat-stable lipid transfer protein 4
• Associations between specific pollens and foods, such as:
  • Grass allergy and peaches, oranges, celery, tomatoes, and melons 3
  • Ragweed allergy and melon, cucumber, banana, and zucchini 3

Diagnosis and Treatment

Diagnosis of OAS is confirmed by a positive history and positive skin-prick test result triggered by the food's fresh extract 3, and treatment centers on avoidance and consideration of self-injectable epinephrine 4