The comments I usually get are about the nicotine (never have heard mention about the thousands of other chemicals).
Pure Nicotine Inhalation Doesnt Cause Cancer
The most notable thing about e-cigarettes for scientists and doctors looking at e-cigarettes is that unlike in tobacco analogues, the nicotine consumed is in pure form. To investigate the effect of this, scientists subjected lab rats to pure nicotine in twice the quantities consumed by even heavy smokers. As if this wasnt enough, they did it for 20 hours per day, five days per week, for two years.
For a smoker to consume this much nicotine, he or she would have to chain-smoke, but with two cigarettes in their mouth at any one time, and only sleep four hours per night to accommodate their Goliath habit. At the end of the study, the heavily nicotine-addicted rats didnt have more tumors or die more frequently than the control group of rats (who breathed ordinary air). In fact, the only difference between the two groups was that the nicotine-consuming rats lost a little weight. This study is one important piece of evidence that shows that the other chemicals in tobacco smoke cause cancer, not nicotine.
Long-term effects of inhaled nicotine. [Life Sci. 1996] - PubMed - NCBI