A common cross-reaction is between birch pollen and stone fruit/kernel fruit such as apples, cherries, and pears. If you have a pollen allergy and have experienced an itchy mouth or throat after eating fresh fruit or raw vegetables, you may have Oral Allergy Syndrome (OAS).

OAS, sometimes also called Pollen-Food Allergy Syndrome (PFAS), is usually a temporary and relatively mild condition due to cross-reactivity. Some plant foods contain proteins that are similar to the proteins in plant pollen, so for people with OAS, their immune system mistakes the food proteins for the pollen proteins, and they’ll then have a reaction. It is important to remember that not everyone who is allergic to birch pollen reacts allergically to stone and kernel fruits.  

In OAS, the immune system mistakes food proteins for pollen proteins, causing an allergic reaction.