@Mark 85: Nic's not really harmful on its own. One of the reasons we wean ourselves down is cost, which becomes especially apparent if you mix your own. Interestingly, the LD50 (lethal dose @ 50% fatality) of pure nicotine and pure caffeine is very similar. Admittedly, nicotine is more readily absorbed on the skin.
As an aside, nicotine is not particularly addictive on its own either. It's when it interacts with the MAOIs and other components of tobacco that it grabs you. The rhetoric has made "nicotine" synonymous with "smoking" which is rather unfair as it's the tar and toxins that kills.
Keep your atomiser moist and the temperature down below 410 degrees (Fahrenheit) and you'll be mostly toxin-free. There will still be a few TSNAs in the base nicotine, as the extraction methods make this unavoidable, but they're such small amounts compared to smoking as to make them a negligible risk compared with continuing to smoke. Synthesising pure nicotine is hellishly expensive right now.
 Monoamine Oxidase Inhibitors, a form of anti-depressant which, along with other compounds present, amplify the addictive properties of smoking tobacco.
[2[ Tobacco Specific Nitrosamines, carcingogens present naturally in tobacco leaf from which pharma grade nicotine is derived. These are also present in the same low concentrations in pharmaceutical nicotine preparations such as gum and inhalators.
 Chronos, an obsessive gobshite always going on about the advantages of vaping. Sorry about that. I'll shut up now.