I've just been reading an article from The Independent in which various well educated scientists, doctors etc have stated that there is now evidence that e-cigs damage cells. They are NOT a healthy alternative to smoking, and yet they are being promoted on our TVs in the same way that conventional cigarettes once were
Public Health England just released a report, quite controversial, that stated they are about 95% safer by their estimates, according to the well-educated scientists that put it together. One article in the Independent isn't really a very good sweep of the scientific evidence.
So, they are likely to be 'healthier', not healthy per se.
Cell studies are really not very good ways of seeing if things are going to cause cancer in 40 years time. If you read the paper, it says that in the conventional cigarette test on the cells, they couldn't make it past 24 hours as they were all dead. The e-cig liquids kept on being put over the cells for weeks and weeks before significant damage was shown.
The reporting of this paper in media outlets, and the conclusions, were outrageously unscientific. Ben Goldacre could have a field day.
As for teens smoking- what we have to ask is not whether some teens use e-cigs (they will, the same ones who would have experimented with regular cigarettes) but whether overall there is less smoking as a result of e-cigs- all the evidence is that smoking rates have never been lower in teens and a paper came out recently that showed teen smoking rates are higher in states in America which have banned e-cigs, blowing the 'gateway' hypothesis out of the water.
Of course it is better to quit and stop altogether, but not inhaling carbon monoxide and tar on a daily basis IS a public health achievement IMO.