This is all strictly hypothetical (of course!), but just how much
long-term damage could two and a half years of heavy marijuana smoking
cause (especially to someone with pre-existing allergy problems)?
Basically, I guess the question is: can it cause permanent damage?
Let's say someone smoked just about everyday for a couple years, ten
years ago, developed a bad sinus infection during the heavy smoking
period, and hasn't gotten back to normal since?

It's one of the things I find frustrating about sinusitis in general:
once they are sensitized, it just never seems to return to normal.