Note – You can find a more recent and in-depth version of this post here: Propylene Glycol in E-Cigs: Is PG dangerous to inhale?
When it comes to recreational nicotine delivery, other than one notable exception, almost every component has been considered suspect. Propylene glycol (PG), the liquid which when heated in electronic cigarettes gives rise to a tangible vapor, a smoke-like volume, has not been targeted by anti-nicotine activists nor have any notable health scares surfaced in the popular media.
Perhaps it is because PG has been studied for over 70 years and no evidence of danger to humans has been found. One of the most recent studies (discussed here by Brad Rodu) which involved subjecting dogs and rats to high concentrations of PG in an aerosol exposure found that the results confirmed the long standing categorization of this substance as “generally recognized as safe”.
Not all of these studies have been either on humans or on the effects specific to inhaling PG. However, many of the studies in industrial settings have used much higher levels of exposure than any electronic cigarette user could attain. The only caveat to this is that since e-cigarettes are relatively recent we have no certainty as to the risks that might attend decades of vaping.
Since we do have a huge and growing population of vapers, we would already know that there are no serious short term complaints associated with daily exposure to PG. There will, of course, always be a few people who will find vaping irritating but that is not any indication of general risk.
What we do know is that based on almost a century of considerable research, it is unlikely that there will be serious long term effects. And we can say with certainty that there is no possibility that these effects could in any way approach the long term effects of tobacco smoking (The same comparison is true in regards to 2nd hand smoke: whatever danger there is to humans from 2nd hand tobacco smoke is magnitudes greater than any possible harm from 2nd hand e-cigarette vapour.)
Apart from the lack of any obvious health risks found in research on PG, one of the reasons there has been little debate about its safety is that it already exists throughout the marketplace in everything from food to pharmaceutical products, and in a number of aerosol products including asthma inhalers and air disinfectants. A very readable online resource (page since removed) on the many applications of this substance has put together by the PG manufacturers who belong to the European Chemical Industry Association.
Though it is quite likely that in the future there will be more e-smokers with no previous experience of nicotine use, at the present time, most e-smokers are ex-smokers. As such, vaping represents harm reduction at its best – users voluntarily switching to a safer but yet pleasurable mode of drug delivery. E-cigarettes satisfy precisely because the PG fueled nicotine delivery is so similar to smoking.While there are reasonable concerns in regards to product quality and consistency, any of the typical components of e-cigarette vapor delivery process are not worth worrying about.
Update: Lene Thorson has kindly pointed us to an article in Time Magazine which points out that Propylene Glycol may be:
‘A powerful preventive against pneumonia, influenza and other respiratory diseases.’
Source: Time Magazine (Unfortunately this source no longer exists)