This is VERY fascinating to me. My mother and her other son my half-brother were wracked by allergies (to the extent of needing the extensive series of anti-allergy injections to function in the case of the brother). I was both a determined thumb-sucker and a nail-biter (I confess — I still do it at nervous intersections). And while I have hay fever here and sadly painful allergies in CA and other places, it is much, much milder than theirs. Like I say, fascinating.