Oral Allergy Syndrome (OAS) aka Pollen-Food Allergy Syndrome, is caused by the immune system in someone with an allergy to a pollen, mistaking protein in the pollen with a similar protein in some fruit, vegetables and nuts. This is known as cross-reactivity.
OAS usually begins in adulthood and for the majority, cross-reactions to food are very mild and affect the mouth only. Symptoms of OAS may include itching or swelling of the lips, tongue, throat or roof of the mouth. Anaphylaxis is very rare.
Heating or digestion usually destroys the allergens causing these reactions. Therefore, affected individuals can usually eat fruits or vegetables that have been cooked, baked, or canned. The OAS-causing protein is often found in the skin of the produce, so eating peeled vegetables or fruits may also reduce symptoms.
However, OAS symptoms may be worse when there is a lot of the pollen you are allergic to in the air.
Diagnosis
Confirming a diagnosis of OAS usually requires a ‘prick prick’ test. This is where a skin prick test is done using fresh fruit and vegetables. However, the combination of pollen allergy and the OAS symptoms is usually sufficient to make the diagnosis.
What pollens cause OAS?
*Allergy to the pollen from Silver Birch trees is the most common trigger of OAS, with around 25% affected.
Foods associated with birch pollen allergy
Fruits
Apples, kiwi, apricot, peach, pear, plum, prune, cherry, nectarine
Vegetables
Carrot, celery, parsnip, potato, tomato, parsley, coriander, green pepper, fennel, dill, peanut, peas, lentils, beans
Nuts
Hazelnut, walnut, almond, Seeds: Sunflower
Other pollen allergies associated with OAS are to grass, and to olive trees. Some people may have OAS from a combination of grass and birch allergy.
Foods associated with grass pollen allergy
Orange, kiwi, watermelon, melon, tomato, potato and peanut.
Foods associated with olive pollen allergy
Pear, peach, kiwi, melon and nut.
*Information supplied by Dr Vincent St Aubyn Crump
For more information, see:
Oral Allergy Syndrome FAQ - Australasian Society of Clinical Immunology and Allergy (ASCIA)