Comment by jandrewrogers

Anecdotally, this is insufficient to explain the evidence.

I have approximately no allergies but was exposed to a very diverse and not sterile environment from early on, with other siblings being similar. I have two brothers close to my age that did have significant and in some case deadly allergies, who were born and raised in the same environment.

Among my siblings, it is a completely mixed bag of sensitivity. Some were highly sensitive to many things, others were sensitive to almost nothing. If mere exposure to non-sterile environments was sufficient then we should all have had similar sensitivity to allergens but the variance in fact was quite high.