Juul, a discreet, stylish e-cigarette introduced by the innovative vaporizer company Pax Labs in 2015, may be too cool for its own good.

Juul dominates the U.S. market, accounting for 73 percent of e-cigarette sales as of September. But the same features that appeal to adult smokers interested in switching to a much less hazardous nicotine habit—sleek design, convenience, flavor variety, cost-effectiveness—also appeal to teenagers. And that has provoked the ire of federal regulators.

The device, which resembles an elongated flash drive and comes in black, silver, blush gold, or turquoise, can be quickly charged in a USB port. When you pick it up, an indicator light tells you how much of the charge is left.

The starter kit, available for $50 from Juul's website (which uses age verification to ensure buyers are 21 or older), includes a charger and four pods containing a 5 percent nicotine solution in mint, crème, mango, and Virginia tobacco flavors. Each pod is roughly equivalent to a pack of cigarettes, and a four-pack goes for $16, so switching to Juul slashes costs for smokers as well as disease risks.

Food and Drug Commissioner Scott Gottlieb recognizes Juul as "a viable alternative for adult smokers who want to get access to satisfying levels of nicotine without all the harmful effects of combustion." Still, he worries that an "epidemic" of underage vaping shows "these products are too appealing to kids." The trick, which no one has accomplished yet, is making a product less attractive to teenagers without also making it less attractive to adults.