Propylene Glycol – is it Safe?
You may have noticed that Propylene Glycol is an ingredient in eliquids. Naturally, when giving up one thing because it is toxic (cigarettes) few amongst us would want to replace that with something that was just as bad.
Propylene Glycol is a major ingredient in e-cigarettes because it principally produces the 'smoke-effect' vapour at low temperatures. This is how the smoke generating machines, for example used to train firefighters, or in fog machines, were able to operate. It has been long used in a huge range of products, including toothpastes and moisturisers. And because of this it's been tested for safety. Yes, it is considered safe at the exposures we encounter and there is no evidence at all of toxicity in the ecigarette.
But, even if it did have a small toxicity, would that actually mean anything anyway? Ecigarette users are usually ex-smokers or people looking to cut down smoking, and to this group the issue is relative harm reduction. If I reduced the total harm by 99% I wouldn't, as an ex-smoker, personally be concerned about the remaining 1%. I would be more concerned about trying to make that 1% go away and then end up with a product that was so ineffective I went back to cigarettes. No one has attributed the lethality of normal cigarette smoke to its propylene glycol content, and yes, tobacco companies have long added propylene glycol to their cigarettes. If you were already a smoker, then you were already inhaling this molecule. The toxicity of smoking is based on the combination of other substances produced in combustion, and the propylene glycol does not play a significant role in this.
So when looking at the ingredients on an e-liquid, it is perfectly natural to look at the chemical names and worry about them, but it is in reality a tiny fraction of the approx 600 ingredients added by tobacco companies to normal cigarettes, and that's before any combustion introduces additional ones. Source