Anaphylactic Allergies: More Than Peanuts

…In northern Europe, people react to the uncooked flesh of apples, whereas in the south it’s the skin that sets them off, whether it’s cooked or not. What could be the cause of this strange invisible dividing line that skims across south-west France, cuts through Italy close to Florence, and continues eastwards through the middle of the Black Sea?

Significantly, this line marks the southern limit of the birch tree, a plant whose pollen is one of the causes of hay fever in northern Europe. Clues for this link lie in the different proteins found in various parts of the fruit: the flesh harbours an allergenic protein called Mal d 1, while the skin is relatively rich in Mal d 3. The structure and composition of the Mal d 1 protein strongly resembles the allergenic protein Bet v 1 found in birch pollen. This means that people who suffer from birch pollen allergy may be primed to overreact to Mal d 1 - explaining the prevalence of the allergy to apple flesh in this region.

via Food allergies get curiouser and curiouser - health - 29 July 2009 - New Scientist.

I’ve seen many peanut-free zones but never an apple-free or melon-free, here in Illinois.  Since there are many communities here from different genetic backgrounds, I wonder if that means that these anaphylactic reactions are more environmental in terms of what people actually react to. i.e. It is a tendency to react, not to anything specifically.