I have allergy, asthma, colitis ulcerosa. I'm allergic to hay, pollen of trees and grasses, dust mites, cat saliva, etc. I've lived in countryside till my 20s, then moved to a big city.
My allergies got better when I moved to a city (probably because there's less allergens), but when I return to the countryside it's still bad (usually it's the worst for the first few days). At least it's not as bad as when I was young (I usually spent a few weeks each year at hospital because of asthma befoer I got 18).
When it comes to air pollution - I grew up during communism in Poland - we had asbestos roof (eternit), everybody was heating their homes with dirtiest and cheapest coal during the winter, and A LOT of people smoked like locomotives. It changed slowly over time.
IMHO there's way too many factors to reduce this to one factor (like sterile environment early on). It probably helps not to have it, but it's not a simple 1-1 relationship.
My allergies got better when I moved to a city (probably because there's less allergens), but when I return to the countryside it's still bad (usually it's the worst for the first few days). At least it's not as bad as when I was young (I usually spent a few weeks each year at hospital because of asthma befoer I got 18).
When it comes to air pollution - I grew up during communism in Poland - we had asbestos roof (eternit), everybody was heating their homes with dirtiest and cheapest coal during the winter, and A LOT of people smoked like locomotives. It changed slowly over time.
IMHO there's way too many factors to reduce this to one factor (like sterile environment early on). It probably helps not to have it, but it's not a simple 1-1 relationship.