Oral Allergy Syndrome (OAS), a type of food allergy, is an allergic reaction that is confined to the lips, mouth and throat. Oral allergy syndrome is due to a cross-reactivity between plant proteins from pollen and fruits or vegetables. When a child or adult with pollen allergy eats a fresh 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.