Despite marketing claims, there’s no proof that e-cigarettes help smokers kick the habit — and they may even hurt their efforts to stop, according to new research.

“The overall cessation argument that’s made to sell e-cigarettes is directly contradicted by the evidence,” said Stanton Glantz, professor of medicine at the University of California, San Francisco and director of the Center for Tobacco Control Research and Education. Glantz co-authored a major review of the scientific literature on e-cigarettes on May 12.

“People who are interested in quitting are more likely to use e-cigarettes but are less likely to quit,” he said. “More people who are using them are failing.”

They might also be subjecting themselves to health risks, according to Glantz.

E-cigarettes deliver a nicotine-containing aerosol popularly called “vapor” by heating a solution usually made up of glycerin, nicotine and flavoring agents. Although the long-term biological effects are unknown, it’s clear that e-cigarette emissions are a source of air pollution and aren’t merely “harmless water vapor,” according to the study.

“While e-cigarettes aren’t as dangerous as cigarettes, they’re still exposing users to high levels of some toxins,” Glantz said. The ultrafine particles — produced by heating the “e-liquid” that’s a mixture of nicotine, propylene glycol or glycerin and other chemicals — in e-cigarettes haven’t been shown to increase heart attack risk, but similar unltrafine particles in cigarette smoke and air pollution have.

“If you have a day with high ultrafine particles, you have a day with more heart attacks,” Glantz said. “That hasn’t been shown to be the case with e-cigarettes, but people need to worry about it until it’s shown that it’s not the case.”

Dual use — with some smoking conventional cigarettes as well as using e-cigarettes — is a major concern. If smokers switched completely from conventional cigarettes to e-cigarettes, there would be less disease caused by nicotine addiction, Glantz said. But as long as dual use is the dominating pattern, it doesn’t matter that e-cigarettes are less toxic.

Investment analysts say dual users are a boon to tobacco industry and the wave of the future, a troubling trend fueled by marketing tactics, according to Glantz.

“It’s completely the Wild West out there,” he said. “It’s like getting into a time machine and going into the ’50s and ’60s.”

E-cigarettes are rapidly penetrating the youth market, he said, and the FDA isn’t doing anything meaningful to stop it.

“The FDA has the legal authority to clamp down on claims that e-cigarettes are good for smoking cessation,” Glantz said. “Those claims should be absolutely prohibited until proven true. The evidence we have is just the opposite.”