Education & Helpful Links Oral Allergy Syndrome (OAS) If you suffer from allergic rhinitis, hay fever, your mouth or throat may become itchy after eating an apple or celery. This reaction occurs because the proteins found in some fruits and vegetables are very similar to those found in pollen. These proteins can confuse the immune system and cause an allergic reaction or make existing symptoms worse. Cross-reactivity happens when the immune system thinks one protein is closely related to another. In the case of allergic rhinitis and foods, the result is called oral allergy syndrome (OAS).The most frequent reaction involves itchiness or swelling of the mouth, face, lip, tongue and throat. Symptoms usually appear immediately after eating raw fruits or vegetables, although the reaction can occur more than an hour later. Rarely, OAS can cause severe throat swelling or even a systemic reaction, called anaphylaxis (an-a-fi-LAK-sis), in a person who is highly allergic.OAS affects up to one-third of allergy sufferers and can occur at any time of the year. Although there is no definitive test for the syndrome, affected individuals often have a positive allergy skin test or blood test for specific pollen, along with a history of symptoms after ingestion of the suspected foods.Different Reactions Based on Different AllergiesIn the case of OAS, individuals react to different foods based on what type of seasonal allergies they are affected by. For instance, if you are allergic to birch tree pollen, a primary airborne allergen responsible for symptoms in the springtime, you may have reactions triggered by peach, apple, pear, kiwi, plum, coriander, fennel, parsley, celery, cherry and carrot. Similarly, people with allergies to grasses may have a reaction to peaches, celery, tomatoes, melons (cantaloupe, watermelon and honeydew) and oranges. Those with reactions to ragweed might have symptoms when eating foods such as banana, cucumber, melon, and zucchini. Cross-reactivity (not OAS) can occur between latex allergies and food items such as bananas, avocados, kiwi, chestnut and papaya.Managing Your SymptomsIf you have symptoms of OAS, avoid eating these foods, especially during allergy season. If you have latex allergy, track foods that might be causing a cross-reaction. Another way to reduce cross-reactions with food is to bake or microwave the food. Eating canned food may also limit the reaction. And, peeling the food before eating may be helpful, as the offending protein is often in the skin.