I wonder if the increase in claimed food allergies isn't due to the population but the food itself.
I have never had any food allergies that I know of until recently. Thinking back, it may have always been there, but I've always been able to eat spicy peppers without any adverse effects. I seem to be allergic to capsaicin, the ingredient in hot, spicy peppers. I remember my hands breaking out in rashes after touching the pre-packaged "catfish" batter we used at work when I lived in NC and worked as a cook. Now, it's cayenne pepper or any kind of dried chili powder that makes me itch from head to toe after eating it. The lunch I bought from the Greek gyro place today tossed some dried seasoning on my food. I felt horrible after eating it and my scalp and ankles are still itching.
I ordered the same thing from that restaurant and bought falafel instead of fries last time... no problems.
The worst problem I have is itching and maybe a mild rash. I can't say I have any other experience with food allergies. Yes, I get the same problem from my own cooking when I use cayenne pepper in my chicken rub. I've been eating that often enough to expect it.