Certain raw fruits and vegetables may cause patients to develop itching of the lips, mouth, and throat. This syndrome, called oral allergy syndrome, is caused by specific proteins in the foods (including melons, bananas, and apples). Importantly, these proteins are heat-sensitive and can be rendered nonallergenic by cooking the food.
For example, patients who have oral allergy syndrome after eating a raw apple will be able to tolerate baked apple pie without symptoms. Due to proteins that are present in both these raw foods as well as certain seasonal pollens, patients who have seasonal hay fever caused by the pollen will develop symptoms after eating the food. Examples of this allergenic cross-reactivity.