Puffing electronic cigarettes would be illegal in most public places across the Bay State — including restaurants and bars — under a Beacon Hill bill rolled out yesterday, but critics argued there’s no evidence that second-hand vapor causes health problems and predicted the increasingly popular devices could be pols’ next tax target.

State Rep. Jeffrey Sanchez (D-Jamaica Plain), the chairman of the Joint Committee on Public Health, said the main goal of his bill is to prohibit the sale of e-cigarettes — battery-powered devices that look like cigarettes, contain nicotine and produce water vapor — to minors under age 18.

“Not very many people know about it, but kids are finding out really quickly,” said Sanchez.

“And that’s what this bill is about. How do we keep electronic cigarettes out of the hands of kids?”

But the bill goes further by banning the distribution of free samples of e-cigarettes and prohibiting using them anyplace it’s illegal to smoke traditional cigarettes, including bars, restaurants and workplaces.

“There’s very little research on these products,” said Margaret Reid of the Boston Public Health Commission, which passed a citywide ban in 2011. “They’re totally unregulated.”

Some 42 Bay State communities have banned using e-cigarettes in public places, according to the state’s Department of Public Health.

But Michael Siegel, a Boston University public health professor who has testified in favor of smoking bans in public places, said similar prohibitions on e-cigarettes are premature.

“Right now, we simply don’t have scientific evidence showing second-hand exposure to vapor in electronic cigarettes is harmful,” said Siegel.

“In fact, there’s quite a bit of scientific evidence that shows it’s unlikely that it causes any substantial health effects for bystanders.”

Siegel compared it to banning grills in restaurants just because cooking fumes contain carcinogens.

“We don’t want to indiscriminately start banning everything out of pure speculation,” said Siegel. “We really want to make sure public health continues to be science-based.”

E-cigarette sales nationwide topped $500 million last year and are expected to reach $1 billion this year. State Rep. Keiko Orrall (R-Lakeville) predicted it’s only a matter of time before Bay State pols take a cut of the revenues.

“The tax issue isn’t a concern right now,” she said, “but definitely it’ll be something that’s looked at in the future.”