I work as a mountain guide, taking people climbing in summer and backcountry skiing in winter. We've had our share of fires and smoke here in Idaho over the years. I use to not worry too much about it, but over time it started to effect me. Last summer I came down with a nasty chest cold due to guiding in the smoke. When I told the boss I was sick because of the smoke he didn't believe me. He thought I was making it up or the cold was unrelated to the smoke. Finally he realized I wasn't going to work if it was smoky, but he said clients cared less and still wanted to get out. I suggested using Air Quality Index as a means of canceling the day if it was in the orange or red... it fell on deaf ears. In the end I feel like it accumulates in the lungs and body and I'm way more sensitive to it now then I was 10years ago. Be careful out there!
I came off the mountain the 2nd day it rolled in; started having chest pains when breathing and unbelievable fatigue (took 2 hrs to go an easy half-mile). I push myself hunting solo, but some things you don't.
Came off the mountain and got a KN95 filter mask. As someone mentioned above, hiking in it sucks, but so does lung damage and low volume monoxide poisoning.
Retired fire lookout here. I now have some lung problems due to smoke. Lived right smack dab in the middle of the smoke 24/7 for 40 season. Try not to do much heavy work in the smoke. The last couple years the area I worked at didn't have a lot of heavy smoke so did okay. So far this smoke hasn't bothered me too much. But the particles of tiny lung destroying ash (?) is what everyone needs to be worried about. Living down under the heavy smoke layer it better than being right in the middle of the smoke layer half way up the mountains and on top of them.
I went hunting close to a big fire a couple years ago and the smoke was brutal. I didn't realize how much it was going to actually affect me, but I could barely make it up the mountain. 2 weeks later went back to the same mountain and mobbed up it no problem. No more hunting in the smoke for me unless I absolutely have to (epic draw tag or something like that).