I worry about the same thing, but I really don't have any choice. I did find a study where rats were kept in a constant mist of PG for quite a long time. They then checked lung tissue, liver, etc. and couldn't find anything seriously wrong. Of course, we're not rats, and we live a lot longer. So, the jury's still out. If we're all still here and happy in 20 years or so, I'd be willing to weigh in with an opinion.
Still, if you don't smoke, maybe better not to take the risk.