It is pretty common to hear people say that our lungs were not meant to inhale anything but fresh air.
This is actually not even remotely true.
Or lungs are meant to do two things, which they do very well...
--Absorb the oxygen in the air we breathe
--Filter out the other stuff in the air we breathe
You lungs were not only made to inhale things other than fresh air, they were designed specifically to do so.
The REAL question is whether or not you are inhaling things that your lungs can not properly handle.
I'm not saying we either are, or are not doing that when we are vaping...
But the short terms results seem to be that our lungs are handling it just fine for the most part.
And if our lungs can handle it fine, there is no reason to say there is anything inherently wrong with inhaling it just because it isn't fresh air.