E-cigarettes ae hurting more people than they are helping, and guess who is feeling the burn? Studies show adolescents and young adults who vape are three times more likely to start smoking traditional cigarettes than those who don’t sample e-cigarettes. Researchers at Dartmouth College’s Norris Cotton Cancer Center say vaping acts as a gateway that leads people to start a real smoking habit. E-cigarette manufacturers have been promoting their product as a way to quit smoking traditional tobacco.

Marketing e-cigarettes as a way to quit or reduce smoking has done damage, mostly to young people, said the study’s lead author Samir Soneji, PhD. Soneji is an associate professor at The Dartmouth Institute for Health Policy and Clinical Practice.

“Although the tobacco industry markets e-cigarettes as a tool to help adult smokers quit smoking, e-cigarette use actually only marginally increases the number of adult cigarette smokers who are able to successfully quit,” he said.

E-cigarette use among high school students soared from 1.5 percent in 2011 to 16 percent in 2015. That year, e-cigarettes were the most commonly used tobacco product of choice for young people in the U.S.

What’s behind the surge in e-cigarette use? Younger, would-be vapers are attracted by fruity flavors and the e-cigarette’s high profile in popular culture. Soneji said that’s the main attraction for youths interested in the devices. The U.S. Food and Drug Administration should focus on those characteristics in its efforts to restrict e-cigarettes, he said.

The Dartmouth study compared current smokers who use e-cigarettes to quit smoking and never-smokers who start smoking by using e-cigarettes and then move on to long-term use of traditional cigarettes.

The scientists estimate that about 2,070 cigarette-smoking adults in America quit in 2015 with the help of e-cigarettes. At the same time, however, an additional 168,000 adolescents and young adults who had never smoked cigarettes started smoking daily after they first began with e-cigarettes. Researchers based their estimates on a model that examined 2014 census data, published literature and surveys on e-cigarette usage.

Smokers who were able to quit using e-cigarettes would likely gain back about five years of their lives, the researchers estimate.  Countering that good news is the impact smoking will have on the non-smokers who would never have started unless they sampled e-cigarettes. Smoking from the time of adolescence and young adulthood on average cuts 10 years off a person’s life.

Scientists added up both sides of the equation and estimated that 2014 vaping could cost a total of 1.5 million years of life in the future. That estimate takes into account the number of years gained for current smokers who use e-cigarettes to stop smoking.

“The harms of e-cigarette use among adolescents and young adults are serious,” said Soneji, who is also an associate professor of health policy at Dartmouth’s Geisel School of Medicine. “Kids who vape are more likely to start smoking cigarettes—notably kids who were otherwise not at a high risk of starting to smoke.”

Read More: Quantifying population-level health benefits and harms of e-cigarette use in the United States