Oral allergy syndrome

Oral allergy syndrome (OAS) or pollen-food allergy syndrome (PFAS) is a type of allergy classified by a cluster of allergic reactions in the mouth and throat in response to eating certain (usually fresh) fruits, nuts, and vegetables. It typically develops in adults with hay fever. It is usually not serious.

OAS is a class II allergy where the body's immune system produces IgE antibodies against pollen; in OAS, these antibodies also bind to (or cross-react with) other structurally similar proteins found in botanically related plants. Therefore, 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. This differs from a class I food allergy where sensitisation to the protein occurs in the gastrointestinal tract, and is produced as a result of exposure to the food itself.

In adults, up to 60% of all food allergic reactions are due to cross-reactions between foods and inhalative allergens. OAS can occur any time of the year, but is most prevalent during the pollen season. Individuals with OAS usually develop symptoms within minutes of eating the food.