SAN FRANCISCO (KCBS ) — A newly released UCSF research study shows that claims made by some electronic cigarette manufacturers—that the devices actually help people quit smoking—are unlikely.

Scientists analyzed 84 research studies on e-cigarettes—battery-operated devices that vaporize a nicotine solution. They have been sold in the U.S. since the mid-2000s and have become immensely popular. They do no emit smoke, which has been part of the attraction to many, including teenagers.

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Dr. Stanton Glanz, director of UCSF’s Center for Tobacco Control Research and Education and a co-author of the Circulation paper, said that the use of such devices is having the opposite effect desired by its users.

“Many people are using e-cigarettes because they are hoping to quit smoking. Smokers who use e-cigarettes are actually less likely to quit smoking than smokers who aren’t using e-cigarettes,” he said.

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While some manufacturers claim the devices help people stop smoking, researchers say that’s unclear because studies show that people tend to use e-cigarettes with combustible cigarettes, rather than as an alternative.

A survey by the U.S. Centers for Disease Control and Prevention also found that the numbers of middle and high school children, who said they tried e-cigarettes, grew from 3.3 percent in 2011 to 6.8 in 2012.

While the health consequences of those particles released from e-cigarettes are still mostly unknown, researchers point out that evidence from previous studies indicates that frequent low- or short-term exposure to similar fine particles from tobacco or air pollution contribute to systemic inflammatory processes in the body that increase the risk of heart and respiratory disease.

“All e-cigarettes deliver lower levels of toxins that conventional cigarettes do; they sill are exposing people to toxic chemicals,” Glanz said.

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Worried about possible health impacts from second-hand exposure, the city of San Francisco, like some other cities across the country, has banned e-cigarettes use in public areas where tobacco smoking is also not allowed.