I don't really know about fog machines. I've certainly had asthma in an environment with fog machines but people were also smoking and that's a definite trigger

I don't really know about fog machines. I've certainly had asthma in an environment with fog machines but people were also smoking and that's a definite trigger. I was on a train a few years ago and had a very weird rapid-onset asthma attack while sitting down. I could feel something weird in the air and taste something very bitter. I looked around and someone was vaping behind me. You're not allowed to vape on UK trains so I guess they turned the "smoke" down? There was no visible cloud. Could easily be a coincidence but the lack of regulation for the "carrier" chemicals is a bit worrying.