E-cigarettes have only been around for about a decade, and it's not yet clear what all the health effects of "vaping" might be. But according to a comprehensive review of research on health effects and usage patterns of electronic cigarettes, they are certainly not "harmless water vapor" as many in the industry have claimed (also see for example this 'study,' published in part by a pro-vaping industry group, or manufacturer's claims that e-cigarettes are safe). It's also unclear if they help people quit smoking, as is often claimed. Many people use both e-cigs and tobacco cigarettes, for example using the former in indoor areas where the latter aren't allowed. For that reason, the researchers, from University of California, San Francisco, suggest they should be subject to the same laws and limitations as tobacco smokes.