Oral allergy syndrome: A type of allergic cross reactivity that occurs in people who are highly sensitive to pollen. The oral allergy syndrome is also known as or pollen-food allergy syndrome and is thought to be a type of contact allergy related to the presence of proteins in certain foods that cross react with allergy-causing pollen proteins. During the seasons that these allergens pollinate, the affected individual may find that when he or she tries to eat fruits, chiefly melons and apples, a rapid onset of itching is experienced in the mouth and throat. Oral allergy syndrome occurs in up to 50% of those who have allergic rhinitis caused by pollen. Symptoms are immediate upon ingestion of fresh or uncooked foods and also include irritation and mild swelling of the lips, tongue, palate, and throat. Cooked fruits and vegetables usually do not cause the reaction. The symptoms usually go away within minutes, although up to 10% of people will develop systemic (body-wide) symptoms, and a small number (1-2%) may experience anaphylactic shock.