In a major scientific review of research on e-cigarettes, University of California, San Francisco scientists found that industry claims about the devices are unsupported by the evidence to date, including claims that e-cigarettes help smokers quit.
The devices, which are rapidly gaining a foothold in popular culture particularly among youth, are marketed as a healthier alternative to tobacco smoking, as an effective tool to stop smoking, and as a way to circumvent smoke-free laws by allowing users to "smoke anywhere."
But in their analysis of the marketing, health and behavioural effects of the products, which are unregulated, the scientists found that e-cigarette use is associated with significantly lower odds of quitting cigarettes.
They also found that while the data is still limited, e-cigarette emissions "are not merely 'harmless water vapour,' as is frequently claimed, and can be a source of indoor air pollution.
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The long-term biological effects of use are still unknown, the research authors said.
The authors analysed 84 research studies on e-cigarettes and other related scientific materials.
E-cigarettes deliver a nicotine-containing aerosol popularly called "vapour" to users by heating a solution commonly consisting of glycerin, nicotine and flavouring agents. E-liquids are flavoured, including tobacco, menthol, coffee, candy, fruit and alcohol flavourings.
Despite many unanswered questions about e-cigarette safety, the impact on public health, and whether the products are effective at reducing tobacco smoking, e-cigarettes have swiftly penetrated the marketplace in the US and abroad in both awareness and use, researchers said.
"E-cigarettes do not burn or smolder the way conventional cigarettes do, so they do not emit side-stream smoke; however, bystanders are exposed to aerosol exhaled by the user," said researchers.