It’s known that repeated exposure to allergens can cause allergic symptoms in people previously without them. For example https://en.wikipedia.org/wiki/Bird_fancier%27s_lung https://en.wikipedia.org/wiki/Farmer%27s_lung

I actually seemed to grow out of hay fever when I was in my early 20s. Perhaps coincidentally this is also around the time I developed an allergy to cannabis from overuse. Wonder if they’re related somehow.