Why does your mouth itch after biting into a fresh apple? Oral allergy syndrome causes tingling and swelling where certain raw foods touch the lips and mouth. It mainly affects people who are also sensitive to tree or grass pollens. The connection works through cross-reactivity. Proteins in birch pollen share a similar shape with proteins in apples. The immune system mistakes one for the other. Researchers used two model systems to measure which foods trigger the strongest allergic response. They also tested how much foods cross-react with each other. The approach identified both major and minor allergens across different food families. Researchers concluded that this method could also predict the allergenic potential of new foods entering the market.