The Food and Drug Administration, meanwhile, has called the use of e-cigarettes and vapes by about two million middle and high school teenagers annually a dangerous epidemic . And last year, the agency warned vaping manufacturers that if they didn’t prove they could keep their products away from underage users, then they’d face penalties.

But the tobacco companies have largely shrugged at the ultimatum.

They are driving awareness and sales via a loophole big enough for the entire industry. Because the research on it isn’t yet sufficient, vape brands aren’t authorized by the F.D.A. to explicitly market their products for their ability to help smokers quit, or “cessation.” So Juul, which controls roughly three-fourths of the American vaping market in the United States, instead simply runs ads in which people happen to describe getting rid of their cigarette habit by switching to Juu l.

And, yes, since there’s plenty of nicotine per puff, you can easily switch from cigarettes. Still, your nicotine addiction isn’t going anywhere.

For grown men and women, that’s an alternative vice of their choice. But the chairman of a National Academies committee that produced a report evaluating e-cigarettes said that vaping’s “adverse effects clearly warrant concern” for young adult users. But in a sea of paid influencer posts, magazine profiles of vapers, and mass-marketed ads, it can be hard for teenagers to fully appreciate the implications: vape liquids contain additives that can form carcinogenic compounds and researchers are concerned about long-term effects .

And now we know Juuling leads to smoking. In one British study, teenagers using these products who weren’t smokers became four times more likely to go on to smoke cigarettes.

If Juul were serious about marketing to adults, it could use pinpointed digital marketing to make sure that those seeing its ads are over 21. Stanford researchers found the company’s launch marketing “was patently youth-oriented.”

Traditional tobacco products have strict regulations. But since Juul is a nicotine delivery device with no tobacco leaf, it is largely free to market as aggressively as possible. You won’t hear cigarette ads on the radio. You could hear from Juul. You can’t see cigarette ads on your televison. But you might see one for Juul, or any of the others.