Nicotine is, itself, pretty damned safe. There is currently no epidemiological evidence to support a direct link between nicotine and cancer. There are reasons

Nicotine is, itself, pretty damned safe. There is currently no epidemiological evidence to support a direct link between nicotine and cancer. There are reasons to believe it can plausibly cause cancer from animal models, but there's no good reason to think that it is more carcinogenic than a boatload of other things. The main reason that nicotine "feels" significantly likely to cause cancer is its association with tobacco. But there's already a perfectly adequate explanation for the carcinogenicity of tobacco. So it's important to resist the affect heuristic[0] which makes us tend to find all things associated with tobacco "cancery". In addition, it's extremely doubtful that you'd get any nicotine second-hand from someone using an e-cigarette. [0] http://lesswrong.com/lw/lg/the_affect_heuristic/ http://lesswrong.com/lw/lg/the_affect_heuristic/