Oral allergy syndrome (OAS) is also called food pollen syndrome-and you'll understand why when you're done reading this page.
The symptoms of OAS: tingling or itching of the lips, mouth (tongue, cheeks, roof of mouth) and throat after eating certain foods. Rarely can develop swelling of these areas too.
What causes OAS: When you're allergic to something, your body is actually reacting to a short part of a chain of amino acids (protein building blocks) in that protein. Sometimes crossreactivity between pollens and foods occurs- that is, there is a protein piece in a particulr pollen that is very similar to a protein chain in a particular food. The body of a person allergic to the pollen is fooled into thinking that pollen is present in the food, and reacts to the food with local tingling and itching where the food has contacted the mucosa. Latex can also cause this confusion or cross-reactivity
Common cross-reacting foods include
Birch: Apple, cherry, pear
Latex: Banana, Avocado, Chestnut
Grass: Potato, melon, tomato
Interestingly, people with OAS to, for example, apples, can often eat cooked apples (applesauce, apple pie, etc) without any problems. This is because some of the protein chains causing allergies unfold and become inactive for causing allergies after being exposed to heat.