As far as intolerances go, we know for sure what some of the contributors are. For instance, mercury (and I think lead) can impair digestion of wheat gluten and milk casein. I consider it likely that others among the multitude of pollutants out there might do similar things. Also microbes can produce toxins that might do similar things, too.

Allergies are likely different, and I don't think all allergies are the same, either.

On the plus side, hookworms are supposed to make it easier to digest gluten.

I don't mean to argue with GMOs potentially causing allergies.

This is Bakers Creek add today