Oral Allergy Syndrome (OAS) Make an Appointment Find a Doctor Ask a Question Reviewed by Carah B. Santos, MD (March 31, 2017) What is Oral Allergy Syndrome? Oral allergy syndrome (OAS) is an allergic reaction that occurs when a person with pollen allergies eats raw fruits or vegetables that have proteins similar to those found in pollen. This condition is also known as “Pollen-Food Allergy Syndrome.” Only a small subset of patients with seasonal allergies will experience OAS. OAS is more common in older children and adults who were previously tolerated these foods. Patients with OAS are most often allergic to birch trees, grass (timothy or orchard), and/or weeds (mugwort or ragweed). Here are the most common foods that cause OAS. Foods That May Cause Oral Allergy Syndrome Pollen Allergy Apple, Apricot, Carrot, Celery, Cherry, Kiwi, Peach, Pear, Plum, Almond and Hazelnut Spring tree pollen: Birch Cantaloupe, Honeydew, Orange, Tomato, Watermelon Summer grass pollen: Timothy & Orchard Banana, Cantaloupe, Carrot, Celery, Cucumber, Honeydew, Peach, Watermelon, Zucchini Fall weed pollen: Mugwort & Ragweed Symptoms Oral allergy syndrome (OAS) symptoms occur immediately after eating certain raw fruits, vegetables, or nuts and are usually limited to the mouth and throat. The most common symptoms include: itching or swelling of the mouth, lip, tongue, or throat. OAS symptoms may worsen during pollen seasons. Most patients with OAS are able to tolerate cooked, processed and peeled forms of these foods. Mild symptoms from eating nuts may indicate a more severe food allergy with a risk of anaphylaxis. See an allergist if you have symptoms after eating nuts. How is OAS Diagnosed? Individuals with OAS have known seasonal allergies. Skin testing can determine seasonal allergies and verify a cross-reactive allergy to fresh fruits and vegetables. Allergy shots may help OAS symptoms; talk with your allergist. Treating OAS Symptoms usually do not require treatment. Follow your allergist’s treatment plan for seasonal allergies and remember to start treatment before your allergy season begins and symptoms appear. Anaphylaxis occurs in less than 2 percent of patients, so carrying an epinephrine auto injector is usually not required. Avoid raw foods that cross-react with your pollen allergens year round. Take oral antihistamine medications to relieve mild symptoms. Bake or cook foods to degrade the protein and eliminate the cross reaction. Eat canned fruits or vegetables during your pollen season. Peel the food as the protein is often concentrated in the skin. Call an allergist when OAS Symptoms: Cause significant throat discomfort Get progressively worse Are caused by nuts Get general allergy season tips. Programs & Services Allergy Treatment Programs (Pediatric) Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.