A new study suggests teens who try e-cigarettes are much more likely than their peers who don’t use the devices to try regular cigarettes.

Among teens who did not use regular cigarettes but had tried e-cigarettes at the start of the study, 20 percent said they smoked their first regular cigarette one year later. In contrast, only 6 percent of nonsmoking teens who had not used e-cigarettes at the beginning of the study had tried regular cigarettes a year later.

“E-cigarettes had a risk-promoting effect for onset of smoking,” the University of Hawaii researchers wrote in the journal Tobacco Control.

The study included more than 2,000 high school students, who were asked in 2013 and 2014 whether they used e-cigarettes or regular cigarettes. The students were also asked questions to measure a number of other factors including their rebelliousness and willingness to seek out new experiences.

Among the students, 31 percent had tried an e-cigarette at the beginning of the study. All students who tried e-cigarettes were more likely to try traditional cigarettes, no matter how often they used e-cigarettes, the Los Angeles Times reports.

The researchers found 10 percent of students who had not used e-cigarettes by 2013 tried them by 2014. Students were more likely to try e-cigarettes if they had the impression that the devices were less dangerous than regular cigarettes.

The study found e-cigarette use was not associated with a decrease in cigarette smoking, the article notes.

“For teens the findings mean that they cannot assume that e-cigarettes are harmless,” lead researcher Thomas Wills said in a news release. “Using e-cigarettes increases the likelihood of starting to smoke cigarettes, which are not good for you. For parents, you can’t assume that it doesn’t matter whether kids use e-cigarettes. It does matter.”