On the one hand, the studies performed so far — small, short term, preliminary studies — have shown that e-cigarettes are modestly effective at helping smokers quit smoking. Their vapor contains the same cancer causing chemicals as cigarettes, but at much lower levels. Vape solutions contain nicotine along with propylene glycol and food-grade flavorings that, when eaten or drunk in small quantities, are not very toxic. On the other hand, nobody knows the health effects of breathing in these chemicals, especially not if it's done several times a day, for years and decades on end. And nicotine itself is not harmless; it's known to affect brain development in children and adolescents. Cigarettes are rarely seen inside public buildings anymore, but e-cigarette use in bars and clubs is already becoming normal. Maybe because of this, non-smokers are starting to use e-cigarettes. The Centers for Disease Control has reported that the percent of middle and high school students using e-cigarettes doubled from 2011 to 2012; part of this was among kids who also smoked cigarettes, and some among kids who used only e-cigarettes.