[trentlott]

Well, it depends.

As far as I remember, the vehicle is propylene glycol. It isn't biologically inert, and I'm not sure how much work has been done to study buildup within the lungs or combustion products. Combine that with dodgy sourcing allowing metal contamination.

It seems more or less the definition of trading the devil you know for one you don't.

[tonypace]

There are a lot of studies about inhaling PG in the context of smoke machines (in bars, generally). It reduces lung function, but not permanently. No more serious harm seems to be indicated.

[EpicEng]

Also, PG has been used in ventilation systems as an air sanitizer for decades. Not a 1:1 comparison given the massively increased volume papers get, but it's something.

[singingfish]

There's literature back to the 1930s about workers inhalation of VG and PG vapour in volume in an industrial setting. From memory, there are consequences but not associated with the chronic degenerative health conditions associated with cigarette smoking. An examination of the molecular biology of VG and PG suggests its quite difficult to find bad things they would do that would be associated with the chronic degenerative health conditions associated with smoking.