Talk about a double-edged sword. E-cigarettes may have started to become popular because of cigarette smokers who want to quit the habit and found the device helpful, but a new study has revealed that e-cigarettes could also start teens smoking actual cigarettes.

The study looked at data collected the U.S. Centers for Disease Control and Prevention's National Youth Tobacco Survey of about 38,000 middle school and high school students. Of that number, 17,000 were surveyed in 2011, and 22,500 in 2012.

The study, conducted by Lauren M. Dutra, Sc.D., and Stanton A. Glantz, Ph.D., researchers from the University of California, San Francisco's Center for Tobacco Research and Education, and published in JAMA Pediatrics, found that in 2011, 3.1 percent of teens who participated in the survey had admitted to trying e-cigarettes at least once. However, 1.7 percent of them admitted to using them together with regular cigarettes. In 2012, 6.5 percent of the teens admitted to trying e-cigarettes. Of this number, 2.6 percent used the e-cigarettes together with regular cigarettes. In the 2012 survey, 2 percent were already e-cigarette users.

The Centers for Disease Control and Prevention defines e-cigarettes as, "battery-powered devices that provide doses of nicotine and other additives to the user in an aerosol. Depending on the brand, e-cigarette cartridges typically contain nicotine, a component to produce the aerosol (e.g., propylene glycol or glycerol), and flavorings (e.g., fruit, mint, or chocolate)." They contain potentially harmful ingredients, such as irritants, genotoxins, and animal carcinogens.

In its Weekly Notes, the CDC emphasized that e-cigarettes are generally not marketed for therapeutic purposes and remain unregulated by the Food and Drug Authority. Most states do not restrict sale of e-cigarettes to minors. 

Potentially harmful constituents also have been documented in some e-cigarette cartridges, including irritants, genotoxins, and animal carcinogens. E-cigarettes that are not marketed for therapeutic purposes are currently unregulated by the Food and Drug Administration. And in most states, there are no restrictions on the sale of e-cigarettes to minors. The CDC also mentioned that 1.78 million middle and high school students in the US use e-cigarettes, and that one in every 10 high-schoolers have smoked an e-cigarette. E-cigarette sales have hit $1.5 million in 2013.

These findings, as well as other numbers generated by the CDC, raise questions as to whether e-cigarettes are actually harmful to public health, despite good intentions. It has certainly helped many long-time adult smokers to limit their smoking, but its use by teens, who are presumably not yet hooked on smoking, is troubling.

"We are seeing the use of e-cigarettes among adolescents rapidly increasing, and it doesn't seem like they're using these products to successfully quit smoking," said Dutra, a postdoctoral fellow at the Center for Tobacco Research and Education at the University of California, San Francisco.

There have been efforts to control the marketing and distribution of e-cigarettes in some parts of the country. New York City, Chicago, and Los Angeles have already banned e-cigarettes in certain public places. Last September, 40 state attorney general petitioned the federal government to regulate e-cigarettes that target young people in their marketing through the use of fruity flavors and cartoon-like advertising.

Some critics of the study, however, say that it is hasty to conclude that e-cigarettes could be the gateway to smoking real cigarettes, since further and more detailed study need to be done. Dr. Michael Siegal, a professor of community health sciences at Boston University School of Public Health who has previously spoken in favor of e-cigarettes, said that that there was no clear evidence to prove that e-cigarettes lead to smoking.

"The authors seem to have an axe to grind," he said. "I could equally argue that what this study shows is that people who are heavy smokers are attracted to e-cigarettes because they are looking to quit," said Siegal.