VAPING will do more harm than good by introducing teens to conventional cigs, says research.
Experts also found their use by adults to try to kick the habit led to only a small number managing to give up.
Professor Samir Soneji, of The Dartmouth Institute for Health Policy and Clinical Practice in New Hampshire, whose team looked at US tobacco-use surveys, said e-cigs could lead to more than 1.5million years of life lost because young adults end up smoking.
He said effective national, state and local efforts are needed to reduce e-cig use among youths and young adults if they are to provide any overall good in future.
He said: "E-cigarettes will likely cause more public health harm than public health benefit.
"Unless ways can be found to substantially decrease the number of adolescents and young adults who vape and increase the number of smokers who use e-cigarettes to successfully quit smoking.
There are fears that kid-friendly-flavoured e-cigarettes will lead to young people smoking tobacco cigarettes"We also need to close the regulatory gaps that make e-cigarettes appealing to adolescents and young adults by reducing the availability of kid-friendly flavours - such as fruit-flavoured e-cigarettes - and issuing product standards that reduce the level of known toxins and carcinogens in e-juice."
He added: “E-cigs will likely cause more public health harm than benefit.”
In the UK more than a million people are currently using them to stop smoking.
And there are calls for the electronic devices to be sold in hospitals to help patients ditch cigarettes for good.