When an apple resembles a pollen allergen
For some people with birch-pollen allergy, the immune system has already learned to recognize a birch protein. Certain proteins in apples have similar molecular features, so the same pollen-specific antibodies can bind to them. This mistaken match is called cross-reactivity: the immune system responds to a related protein as though it were the one it encountered before.
The reaction is often called pollen-food allergy syndrome, or oral allergy syndrome. It usually begins soon after a person bites into a raw apple. Itching or tingling may appear on the lips, tongue, roof of the mouth, or throat—the areas that first touch the fruit.
Why cooking can make a difference
Many of the apple proteins involved are fragile. Heat can unfold or break them apart, changing the features the antibodies recognize. That is why a person who reacts to a raw apple may tolerate applesauce or a baked apple. Peeling may also help some people, since relevant proteins can be concentrated near the skin, but it does not reliably prevent symptoms.
The effect depends on the person and the food: cooking does not make every apple product safe for everyone, and people’s reactions can vary. The practical clue is that a raw fruit may trigger symptoms while a cooked version does not—a consequence of changing the protein, not changing the apple’s pollen-related history.
