Reddit reviews Natural Solutions for Food Allergies and Food Intolerances: Scientifically Proven Remedies for Food Sensitivities

The best theory I've seen put forward is in this book on food allergies and sensitivities. It's got lots of recent research including studies on children with food and peanut allergies.

Of particular note is a comparison between the US and China. Both countries eat about the same amount of peanuts per capita, but China's peanut allergy rate is on par with the rest of the world (quite low) while the US is obviously quite high.

The main difference between the two is the preparation of the peanuts. In China (and I believe many other places) peanuts are mainly boiled or fried while in the US most peanuts are baked.

Baking isn't inherently evil, but the higher heat produces a higher amount of a chemical in the peanuts that's associated with peanut allergies (apologies, I can't find my copy and can't remember the name of the chemical).

It was in the mid-nineties that food manufacturers began switching to baking peanuts (for their consumer-preferred flavor). This was the time that peanut allergies began their rise in the US.

This isn't to say that there may not be other factors within the States that contribute to greater susceptibility to allergies, but this seems to me like the strongest, backed-by-data theory pertaining to peanut allergies.