No studies have been done on the product as a whole in its marketd use. All the bases of e-liquid are considered safe per FDA, and there have been small studies done that show there are no harmful by products when vaped. There is a study that has currently been concluded to my knowledge that they are just looking to get published.
There is nothing “concrete” and like I said the FDA refuses to touch it, but there have been small studies/tests done by independent lab rats that have found nothing harmful aside from the Nicotine itself, which as I said before the side effects of nicotine as im sure youre aware are much like those of long term caffeine use. There are also benefits to nicotine. Its up to someone whos looking at switching to e-cigs to do their research and determine whether or not they would rather keep smoking analaogs, use e-cigs or quit all together. I have read a lot on the subject and have talked to a lot of people, and In my opinion, the risk is extremely low, nearly nothing compared to smoking a real cigarette so I made the switch.
Do we know what long term side effects if any e-cigs have? No, because they have only been around ~5 years now (3-4 years or so here in the US) I know people who have been vaping for 3-4 years now who were not in the best state of health who are now healthier then most. There are doctors in the community who have discussed how peoples overall stats have improved, shown x-rays of a year before and after vaping and how much they have cleared up is amazing. Theres a whole thread of people who started sharing chest x ray of years before and a year or two after of vaping.
In the 5 years of existence to my knowledge there has not been a single report of someone becoming ill from e-cigs or them being related in anyway.
I hope the FDA steps in in some way and tests them, I’d like to see regulation to an extent. I would not like to see phillip morris branded e-liquid that will probably have a million other shit chemical in it, ridiculously expensive kits and liquids, thats what I am afraid of.