[viraptor]

> accustomed to the allergens due to forceful conditions is the best explanation for this.

While desensitization works https://en.m.wikipedia.org/wiki/Desensitization_(medicine) you can't really just force expose someone and hope for the best.

It's a bit correlated to developed countries, but not completely https://waojournal.biomedcentral.com/articles/10.1186/1939-4...

I'd propose a mix of everything but also: e) People don't call things allergies unless they know it's that. I said for decades that I can't eat spinach or I'll have diarrhoea, but learned later that also classifies as an allergy. f) More developed countries have more difference in available cuisines. For example I've not seen a shellfish until I moved out of home, so wouldn't know if I'm allergic to them. g) (probably lots of other factors)