Comment by Retric
4 years ago
Changing rates of testing combined with false positives are presumably part of it. Apparently 10% of people think they are allergic to Penicillin but only 1% test positive and under 0.1% have a significant reaction.
That said, environment is a factor. People in the developing world test positive for fewer though by no means zero allergies compared to their relatives in the developed world.
There's also changes to breeds and varieties in common use. For example, modern wheat has like 20x the histamine response vs older varieties. These kinds of things will also affect different people differently.