Who knew that in today’s classroom, students in middle or high school could sneak a hit of nicotine from something that looks like a flash drive, a pen or lipstick? They can, and they do.

Nearly a quarter of high school seniors say they vape daily, and more than 1 in 10 eighth-graders say they’ve vaped in the past year, according to the 2017 Monitoring the Future survey conducted by the University of Michigan. “Vaping” is done with electronic cigarettes that heat nicotine-infused liquid into a vapor, which is then inhaled by the user. There’s no smoke, just flavored vapor that can smell like strawberry, cotton candy or creme brûlée.

Why so much adult hand-wringing about this adolescent craze? Vaping’s sort of like smoking cigarettes, but without the lung-clogging, cancer-causing tar, right? Not exactly. There’s still a lot we don’t know about the long-term health effects of vaping, one reason why parents and school officials should be more hands-on about reversing vaping’s popularity among teens.

Along with nicotine, vaping liquids contain a mix of additives, including propylene glycol and glycerol. When heated, those chemicals can form carcinogenic compounds. Then there’s the nicotine itself. A recent New York Times article about vaping among teens reported that school administrators increasingly see signs of nicotine addiction among students who vape. One student cited in the story asked her teacher for permission to stand in the back of the classroom and shake her foot when she felt the urge to vape.

Especially worrisome:  growing evidence that vaping among teens leads to smoking cigarettes. America has made massive strides in turning the tide against teen smoking. In the late 1990s, a quarter of high school seniors smoked, according to University of Michigan researchers. Today, that number’s been whittled to 5 percent. Teens who start to vape now are, for the most part, not current or former cigarette smokers. But the 2016 Monitoring the Future study found that a year after nonsmoking high school seniors began vaping, they were four times as likely to have smoked a cigarette as someone who wasn’t vaping.

The disturbing paradox:  For grown-ups, vaping is a means to break away from cigarettes. For teens, vaping’s becoming a gateway to tobacco smoking.

We shouldn’t be surprised. Today’s vaping by the 3-D printer is yesterday’s smoking in the bathroom. But it could steamroll into a full-blown health crisis if parents, schools and public health officials don’t intervene. Vaping may prove to have, or not have, long-term health consequences. But we do know about nicotine and the harm it can do. That alone should be enough to make vaping among teens a trend that vanishes like a puff of creme brûlée.