Oral Allergy Syndrome

Oral Allergy Syndrome

What is it?

Oral allergy syndrome (OAS), a type of food allergy, is an allergic reaction that is confined to the lips, mouth and throat.

OAS most commonly occurs in people with asthma or hay fever, from tree pollen, who eat fresh (raw) fruits or vegetables. Other pollen allergies may also trigger OAS. Adults appear to be more affected than children.


Oral allergy syndrome is due to a cross-reactivity between plant proteins from pollen and fruits or vegetables. A protein on the surface of some fruits and vegetables is similar to the pollen protein and can trigger an allergic reaction. When a child or adult with pollen allergy eats a raw fruit or vegetable, the immune system sees the similarity and causes an allergic reaction.

Interestingly, many patients with oral allergy syndrome can eat the same fruits or vegetables when they are cooked. The cooking process changes the protein enough that the immune system does not recognize the food as being the same as the pollen anymore.

Sometimes foods in the same botanical family will also cause reactions. Examples are potato and carrot, parsley and celery, or apple and pear.


Pollen Type

Potential Cross-reactive Foods


Bananas, melons (watermelon, cantaloupe, honeydew), zucchini, cucumber, dandelions, chamomile tea, echinacea, goldenseal


Apples, pears, peaches, apricots, cherries, plums, nectarines, prunes, kiwi, carrots, celery, potatoes, peppers, fennel, parsley, coriander, parsnips, hazelnuts, almonds, walnuts


Peaches, celery, melons, tomatoes, oranges


Celery, apple, kiwi, peanut, fennel, carrots, parsley, coriander, sunflower, peppers


Celery, pears, apples, almonds, cherries, hazelnuts, peaches, parsley


Bananas, avocado, kiwi, chestnut, papaya