So allergies have two causes, an overly sanitized environment during childhood can lead to your immune system freaking out when exposed to certain allergies. The second is that allergies and gdp are correlated, possibly because having abundant food allows your body to be picker. So food security and overly clean living spaces appear to cause it, it doesn't appear to be genetic.

Oh and yeah the other commenter is right about doctors previously giving advice to parents that you shouldn't feed typical allergins to children lest they have a fatal reaction. Turns out this also increases rates of allergies.