I have been following this line closely since I have some pretty bad allergies
and have had since a child.
I grew up in a poor family in the late forties and early fifties.  Making mud
pies, cats, dogs, four siblings, neighbors all over the place, exposed to
everything that came along and had most of the childhood illness's as there
weren't any vaccines in those days.  In other words I wasn't sheltered,
protected or in a "clean" enviriorment.
What is even more interesting is that for a little over two years I had been
symptom free for the most part...then this last year started lo-carb diet and
have been moving in the direction of paleo although not there by a long shot -
and for the last month have had the worst episode of sinus allergies and
asthma attacks that I have had in years...figure that one out!
My wife thinks my diet is causing it.  My doctor says allergies are allergies
and there is no predicting when and where and how intense the attack will be.
Me, I am just glad I have an inhaler so I can survive.
steve