Teens – what cool new trend will they latch onto next? With increased pressure to avoid combustible tobacco products, vaporizers, or e-cigarettes, appear to be gaining a foothold in the cool teen community. But because scientists have nary a clue whether e-cigarettes are safer than tobacco products or just as harmful, the up-tick in their use among teens is cause for alarm. Now, a study by USC researchers finds that teen e-cigarette use is predicted by a couple of familiar factors: Peer approval and use in the home.

The study followed 2,084 11th- and 12th-grade students from January to June of 2014. They were asked whether they’d ever used e-cigarettes or traditional tobacco before, as well as if they were “current” (within the last 30 days) users. They also asked how many of their friends smoked or vaped, whether they approved of it, how many family members smoked or vaped, and the perceived health risks.

Overall, teen smoking is indeed on the decline: Just 18.7% said they’d smoked tobacco at all, and only 5.7% smoked currently. Even vaporizer use, the impetus for the study, is still relatively depressed: 24% of teens have tried them, and 9.6% were current users. As for any “gateway” effect from e-cigarettes to tobacco, evidence is slim: Just 3.2% reported using both vaporizers and tobacco in the last month.

More interesting are the risk factors for e-cigarette use. The most powerful was peer pressure and approval – of the teens who had used an e-cigarette in the last 30 days, 49.5% had three or four friends who used them. After that came family use: 34% of current teen vapers shared a home with someone who used a vaporizer.

Teens seem to agree that tobacco is dangerous, though just under half disagreed that vaping posed similar health risks. Overall, the researchers find the results troubling because the risk factors associated with e-cigarettes use (peer and family use) are identical to those associated with traditional tobacco use.

Though this study produced little evidence, the authors called for further research to determine whether e-cigarette use serves as a gateway to traditional tobacco use in teens.