While many forms of e-cigarette advertising increase the odds that teens will try the devices, a new U.S. study suggests that this generation of digital natives is most enticed by promotions they see online.

Big U.S. tobacco companies are all developing e-cigarettes. The battery-powered gadgets feature a glowing tip and a heating element that turns liquid nicotine and other flavorings into a cloud of vapor that users inhale. To see which e-cigarette ad formats were most persuasive to teens, researchers analyzed data from a recent nationwide survey of about 22,000 middle school and high school students from grades 6 through 12, when youth are typically about 12 to 18 years old. When middle school kids said they routinely viewed e-cigarette ads online, they were almost three times more likely to use the devices than their peers who never saw ads. High schoolers who frequently watched online ads were about two times more likely to use e-cigarettes. "E-cigarette ads use many of the same themes used to sell cigarettes and other conventional tobacco products, such as independence, rebellion and sex," said lead study author Dr. Tushar Singh of the Office on Smoking and Health at the U.S. Centers for Disease Control and Prevention in Atlanta.

Three million middle and high school students said they were current users of e-cigarettes in a CDC survey last year, up from about 2.5 million in 2014, according to a report released this month. For the current study, Singh and colleagues analyzed data from the 2014 National Youth Tobacco Survey, which asked teens about how often they used different types of tobacco products as well as how frequently they encountered ads for these items.