I first experienced mine at 33 - without any gradual changes in the years before that; just suddenly, out of nowhere, full blown hay fever.
One of my relatives had hay fever all her life, until it suddenly disappeared at the age of 42. She had it at 41, she had none at all at 42.
But alternative therapies at least put the thought of causation in you head, which make you track it more than anything else.
Then survivor bias makes random positive results more visible. How many people did alternative treatments not work for? But then, such a result would be inconclusive for dismissing the treatment, right? That means the domain has a natural positive bias if negative results are not weighed equally against positive ones.
I suffer hayfever-like symptoms only when visiting a certain area for a few days, and typically it takes a few days for the effect to kick in. (I live in Sydney, Australia, and the area is about 3 hours drive north of same.) Flora shouldn't be significantly different, though there will of course be some variation. It's the fact that it seems to take 2-3 days to kick in, and effects are mostly prevalent in the evenings, that has me most confused. I considered it may be artificial environmental (something in the living quarters, f.e.) rather than flora, but the effect still occurs when I avoid the abode. It seems to vary slightly throughout the year, but not as much as I'd hope it to be if it's vanilla hayfever. It's very strange, especially as it only started occurring for me about a decade ago - in my mid 30's.
Still, this anecdote is not compelling evidence goop isn't a steaming load of hoohar.