Electronic cigarettes have soared in use among high school and middle school kids, tripling in 2014, while cigarettes have reached an all time low. The report was issued by the Centers for Disease Control and Prevention, which found  4.6 million middle and high school students were current users of any tobacco product, which includes e-cigs despite the fact that it doesn’t burn or contain any tobacco – just the nicotine.

Among high school students, e-cigarette use jumped to 13.4 percent in 2014 from 4.5 percent in 2013, according to the Centers for Disease Control and Prevention. Cigarette use over the same period fell to 9.2 percent from 12.7 percent, the largest year-over-year decline in more than a decade. Among middle school students, current e-cigarette use more than tripled to 3.9 percent in 2014 from 1.1 percent in 2013, while cigarette use remained unchanged, the CDC said.

So, should we be excited by the news or, on the contrary, more worried? Tobacco control advocates fear that e-cigs are a “gateway” that promote an unhealthy lifestyle and make kids prone to addiction later in life. Sort of like wearing a seat belt, but driving faster because you feel safer.

“Nicotine exposure at a young age may cause lasting harm to brain development, promote addiction, and lead to sustained tobacco use,” Dr. Tom Frieden, director of the CDC, said in a statement.

Mitch Zeller, director of the Food and Drug Administration’s tobacco division, said the data “forces us to confront the reality that the progress we have made in reducing youth cigarette smoking rates is being threatened.”

Just as well, however, the data could be interpreted as a sign that smoking rates fell because young people took up e-cigarettes instead of traditional cigarettes. The CDC said nearly half the students used more than one tobacco product. The most popular was e-cigarettes, followed by hookah. Cigarettes came in third place followed by cigars, smokeless tobacco and pipes.

A  meta-study which examined 81 e-cigarette studies found that these are less harmful than tobacco cigarettes, and that their introduction reduces the number of tobacco-related deaths. The long term effects of e-cigarette use are, however, largely unknown. Because of this, the World Health Organization and national authorities are considering policies to restrict their sales, advertising and use given the absence of evidence that they help smokers quit, and the way they are being exploited by the tobacco industry to target children.