Since they first hit the U.S. market in the mid-2000s, electronic cigarettes, or e-cigarettes as they are commonly known, have become wildly popular. Some doctors and researchers are supportive, saying that if all cigarette smokers quite smoking and switched to e-cigarettes, tobacco-related illnesses and deaths would drop dramatically. However, tobacco experts at the University of California-San Francisco published a brief review suggesting that optimism for health benefits from rises in e-cigarette use be tempered.

The review, authored by Rachel A. Grana, Pamela M. Ling, Neal Benowitz, and Stanton Glantz, examines whether overall public health will increase with the surge in e-cigarette use.  E-cigarettes are battery-powered devices that deliver nicotine to the user by creating an aerosol from a liquid mixture. The aerosol, although created by heating, contains no combustion products. Although marketers say that e-cigarettes are entirely safe, some experts cite the liquid ingredients for advising that they are not necessarily safe.

“As we’re getting better and better understanding of the chemistry of these things, they’re looking worse and worse,” said Stanton Glantz, director of UCSF’s Center for Tobacco Control Research and Education and senior author of the Circulation review. “You can be a lot less bad as a cigarette and still be pretty bad.”

The liquid for e-cigarettes typical contains propylene glycol, plant-derived glycerin, chemical flavors, and nicotine. The aerosol from these liquids delivers lower levels of toxicants compared with cigarette smoke. However, the aerosols still contain particulates, toxicants, and carcinogens. There are no studies yet that have examined the long-term effects of e-cigarette use so claims that they only deliver harmless water vapor are inaccurate, according to the review authors.

The researchers are also concerned with the way e-cigarettes are marketed, particularly toward youth.  “E-cigarettes are aggressively advertised on television, on the radio, on the internet, and in magazines,” they wrote. In the one year period between 2011 and 2012, e-cigarette use more than doubled among children, increasing from 3.3 percent to 6.8 percent. In addition, research shows that a large number of e-cigarette users do not quite smoking cigarettes but engage in “dual use.” A total of five population-based studies all found that e-cigarettes are ineffective as smoking cessation aids.

Even so, the authors do encourage dual users to give up cigarette smoking before trying to quit e-cigarettes.

The review appears this week in the journal Circulation, published by the American Heart Association.