Many Thanks for the info on this important topic.
I think some of the posts are being a little hard on researchers as at least some of the analyses refered to in this thread are two-a-penny commercial lab reports rather than real research. These probably only cost a few hundred dollars and so are limited. A much more rigorous analysis can be found at
http://healthnz.co.nz/RuyanCartridgeReport21-Oct-08.pdf. Even this is not, strictly speaking, a formal scientific study (not published or peer-reviewed and funded by Ruyan) but is the closest I've seen to actual research on eliquid analysis.
The MSDS can seem alarming but everything is toxic depending on the concentration, even pure water (yes people have died from drinking too much water). So the important thing is to look at the LD50 numbers to put this into the correct perspective.
For example for PG the LD50 is:
Oral
Rat
20000 mg/kg
LD50
This LD50 means that 50% of rats will die if they consume orally at least 20 grams of PG for every 1 kg of body weight. So the average size rat (500g) would need to drink 10 millilitres of PG before it was toxic (at least half of the time). By comparison the rat LD50 for seawater is 3000mg/kg, so PG is about seven times safer to drink than seawater. Pure water has an rat LD50 (greater than 90ml/kg).
There is a real need for more rigorous research like the report above. Problem is this is really difficult to do even if you had unlimited research funds. Trying to work out exactly what all the constituents are in e juice is very difficult, let alone trying to work out what is converted in vapor and what interactions occur in the mouth, lungs, blood etc. A complete assessment is very difficult to achieve (have a quick look at the limitations/disclamers on any meds you have or on products like nicobate, champix, varenciline etc.). Suprisingly little is known about the health consequences of many pharmaceuticals and we generally rely on some authority to provide us a determination that it is safe (FDA etc), although they dont know any more than the available research, more of a best guess based on the limited evidence and excluding the more obvious problems.
So while there is a real need for more research, the avaible evidence referred to in this and other threads indicates that the constituents in eliquid become toxic at levels 100 to 1 million times greater than the concentrations in ejuice. As reported, these levels are actually much lower since many constituents are exhaled following inhalation. From an admitedly brief reading, the main concerns seem to be the unknown toxicty of some of the flavours used, although even these may not be a problem at common vaping temps. Still as often advised in these forums, best practice is to limit the flavours you add to ejuice.
One thing you can do while waiting for the research to catch up with you is use your body as a test tube and do your own analysis. Like me you probably smoked about a packet a day. Like me, you probably noticed almost immediately you didnt constantly crave a cigarette and smell like an ashtray. When you did try one you couldnt take more than a few puffs. Your brain had already began to disassociate the unpleasant and toxic effects of cigarette smoke from nicotine. At this point, cigarettes were history and you were a member of the Vaping Nation.
Then around two weeks later you noticed your smokers cough had disappeared. After 1 month or so people began commenting that your skin tone and texture had changed dramatically, you actually look healthy. Then you began to notice you could enhale a rapid deep lung full of air without coughing. A little later you were late for a meeting and ran up a couple of flights of stairs. After sitting down it began to dawn on you that something was missing. That's it...you werent puffing, wheezing, sweating profusely.
You dont need a doctorate to work out that vaping nicotine is therefore about 23.02 zillion times safer than smoking tobacco. You also shouldnt need a doctorate to understand that vaping isnt 100% safe, nothing is. Can it be made safer, of course it can be but we need to wait for more research. Meantime I think the ECF forums like this are the best place to keep yourself up todate with current knowledge about health issues and research.
PS, in the orignal post 'dehydrate' should be changed to hydrate. PG is very miscible in water and if you get any on the skin or eyes a splash of water will prevent any irritation occuring.