I recently had the flu for a while, and still smoked once in the very middle of it. Had no problems what so ever(Well, except for having the flu.).

I really don't think that THAT many particles could go through the screen and all the way up the whip, so inhaling anything other than a minute amount of dust isn't that bad. But when you're inside, you are inhaling dust. Outside inhaling dust and pollen and stuff.