I am allergic to most grass, tree and weed pollens, and mold spores. My allergies are bad enough on the Great Plains (changing with seasons) but get much worse when I return to the Great Lakes region where I lived the first 22 years of my life and became sensitized to all the stuff growing between Spring and the return of killing frosts.
Moving to Florida didn't help much. I didn't encounter some of my worst seasonal allergies, but what I had, I had year-round. Visiting Arizona (Phoenix area) did not help much, seems everybody retiring there brought their Eastern and Midwestern lawns and gardens with them.
But moving back to the Great Lakes from Florida was a disaster. Very soon after getting back, I had to step up from antihistamines to desensitization shots, which still did not help all that much. What fixed that problem was moving away again, to the plains, where I had three to five years relief while becoming sensitized to the new (mostly grass) pollens.
It does help to go to places with completely different flora. Two years in China troubled my plant allergies very little, and the always dirty air in the big cities did not bother me near as much. I get relief also in urban and coastal areas in southern and eastern Europe, but feel the difference almost immediately moving into agricultural areas where they are growing some of the same things we grow on the plains or in the corn belt.
Going to southern England in the summer was a disaster. It seems most of what we grow in midwestern suburbs are the ornamental plants brought to this country by English colonists.