It resembles a long USB stick, but in reality it is a device that is growing in popularity with teens in a trend that is causing a great deal of concern among authorities. It is called “Juuling,” and it involves using a type of cigarette known as a JUUL that looks like a USB stick and is rapidly taking hold among teens.

Kids as young as 14 are taking to experimenting with the device, prompting the U.S. Food and Drug Administration to address the matter earlier this year. JUULs have replaceable pods that come in multiple flavors, and some media reports indicate that teens have trouble quitting, much like with addictive cigarettes, although there is still a lot we do not know about e-cigarettes in general when it comes to their health and safety.

Back in August 2016, the FDA set limits on sales of e-cigarettes, restricting them to customers 18 and older. However, that has not stopped them from falling into younger hands. The trend has prompted the FDA to send warning letters to dozens of retailers over sales of JUUL devices.

“The troubling reality is that electronic nicotine delivery systems (ENDS) such as e-cigarettes have become wildly popular with kids,” reads an FDA statement. “We understand, by all accounts, many of them may be using products that closely resemble a USB flash drive, have high levels of nicotine and emissions that are hard to see. These characteristics may facilitate youth use, by making the products more attractive to children and teens.”