Teens may think that e-cigarettes are harmless, but a new study shows that those who try them could wind up becoming lifelong smokers.

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, examined survey data from adolescents in middle school and high school from 2011 and 2012.

They found that 3.1 percent of them had tried e-cigarettes at least once in 2011, and 1.1 percent regularly smoked e-cigarettes. By 2012, 6.5 percent of them had given e-cigarettes a try and 2 percent were currently smoking them. The researchers found an increase in the odds that young adults who had smoked e-cigarettes or currently smoked them would try smoking traditional cigarettes too.

In 2011, smokers who used e-cigarettes were more likely to try to quit smoking within the next year. But data also showed that young adults who smoked e-cigarettes were less likely to abstain from smoking conventional cigarettes.

An e-cigarette looks similar to a traditional cigarette, but contains cartridges filled with a liquid nicotine solution. Some come in flavors, which makes them taste nothing like traditional cigarettes. Most e-cigarettes have a blue tip instead of a red one that lights up upon inhalation.

“While the cross-sectional nature of our study does not allow us to identify whether most youths are initiating smoking with conventional cigarettes and then moving on to (usually dual use of) e-cigarettes or vice versa, our results suggest that e-cigarettes are not discouraging use of conventional cigarettes,” the authors said.

According to a report released last year by the Centers for Disease Control and Prevention, e-cigarette use has doubled among high school and middle school students, and 1.78 million middle and high school students in the U.S. currently use them. The report also says that one in 10 high schoolers have smoked an e-cigarette.

Bloomberg Industries analyst Kenneth Shea reports that e-cigarette sales hit $1.5 billion in 2013.

The use of e-cigarettes has risen rapidly in the U.S. in the past few years, said Frank J. Chaloupka, Ph.D., of the University of Illinois at Chicago. He noted that some analysts believe sales of these devices could overtake sales of conventional cigarettes in the near future.

“I think there are several factors that are likely to be contributing [to the popularity of e-cigarette use], including the increasingly widespread advertising of e-cigarettes, the availability of flavored varieties, relatively low prices, the perception that they're relatively safe, and, in many jurisdictions, the lack of policies affecting sales and use,” Chaloupka said.

The U.S. Food and Drug Administration can regulate e-cigarettes under current tobacco laws because they deliver nicotine from tobacco. The FDA says on its website that e-cigarettes that are marketed for therapeutic purposes are subject to regulation.

Just this week, the Los Angeles City Council banned e-cigarettes wherever regular tobacco products are forbidden. Lawmakers across the country are faced with similar choices, as the dangers of "vaping" e-cigarettes are largely unknown.

Chaloupka said that e-cigarette use among young people is troubling because it could become a gateway to regular cigarettes for some young adults who would not otherwise become smokers.

“At this point, it's too early to say whether this will be a small problem or a big problem,” he said, adding that adopting polices on e-cigarette regulation could prevent that from happening.

When it comes to e-cigarettes, Chaloupka said the biggest danger is nicotine addiction, as well as progressing to regular cigarettes or other combustible tobacco products. He says another issue is the harmful chemicals in e-cigarette vapor inhaled by smokers and then released into the air and subsequently inhaled by non-users.