The numbers of US teenagers who "vape" is rising, US health officials said Thursday.
According to the Center for Disease Control and Prevention (CDC), over 2 million teenagers used electronic cigarettes (also known as e-cigarettes) in 2017.
In a study, the CDC found that 19.6% of high school students smoke, and most of those smoke e-cigarettes.
However, CDC's Dr. Brian King told Fox News that, "It's possible we have underestimated the extent of e-cigarette use in this survey."
He also noted that many teens call vaping "JUULing" due to the brand's growing popularity, and that the popularity and availability of e-cigarettes had stopped the US' progress in the battle against tobacco.
Many e-cigarettes are flavored, something which appeals to teens, the site noted. However, the products contain nicotine - JUUL's amounts are higher than other companies' - and they can also contain heavy metals.
NBC News quoted CDC's Teresa Wang: "Since 2014, e-cigarettes have been the most commonly used tobacco product among both middle and high school students."
The site also quoted Heart Association CEO Nancy Brown: "Our greatest fear is that this may be a warning sign of a reversal, and in the coming years we may see a disturbing rise in the number of middle and high school students who smoke e-cigarettes."
"The tobacco industry is well aware that flavored tobacco products appeal to youth and has taken advantage of this by marketing them in a wide range of fruit and candy flavors. Their strategy is working too well, unfortunately."
It's not yet clear what the long-term consequences of e-cigarettes are.
E-cigarettes are not allowed to be sold to minors in any state, and some states have a minimum age limit of 21.