But in theory electronic cigarettes can be used anywhere - on planes, trains, in hospitals.

BBC: Electronic cigarettes - miracle or menace?

This growth in interest is exactly what White Cloud Electronic Cigarettes are banking on.

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Electronic cigarettes are battery-powered devices that heat a liquid nicotine solution in a disposable cartridge, creating vapor that users inhale.

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Electronic cigarettes, first sold outside China only over the past seven years or so, have few solid studies attesting to their benefits for helping smokers quit.

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"Further research is needed to assess the potential public health benefits and risks of electronic cigarettes and other novel tobacco products, " said Jennifer Haliski, an FDA spokeswoman.

CNN: Sales of e-cigarettes continue to soar

The trade association for e-cigarettes, the Electronic Cigarette Industry Trade Association, says they make no medicinal claims for their product.

BBC: Electronic cigarettes - miracle or menace?

Ray Story, chief executive of the Tobacco Vapor Electronic Cigarette Association, warned that tax rises on e-cigarettes would only benefit tobacco companies, to the detriment of public health.

CNN: Sales of e-cigarettes continue to soar