The short answer is we don’t know.
Which should be very scary.
And makes me wonder who, if anyone, is regulating anything anymore.
The problem with measuring what a vaping e-cigarette does is that there is no standard for e-cigarettes. The amount of nicotine isn’t even necessarily what’s on the package. Forget about any consistent level of “tobacco-specific nitrosamines (TSNAs), aldehydes, metals, volatile organic compounds (VOCs), flavours, solvent carriers and tobacco alkaloids”
So we’ve got mouse studies that may or may not be relevant. They found that “E-cig vapors… increased bronchoalveolar lavage fluid (BALF) cellularity, Muc5ac production, as well as BALF and lung oxidative stress markers at least comparably and in many cases more than CS (cigarette smoke).” Now, cigarette smoke tended to build up more nastiness over time, but those e-cigs did a ton of inflammation. (More at my blogger site).