The marketing strategy could reverse decades of progress in preventing tobacco use among youth, warned the U.S. Centers for Disease Control and Prevention, which suggested tighter controls on e-cigarette sales to reduce minors’ access.

“The e-cigarette advertising we’re seeing is like the old-time Wild West,” CDC Director Tom Frieden told reporters. “No rules, no regulations and heavy spending advertising the products.”

E-cigarette use among middle- and high-school students soared over the past five years, surpassing use of regular cigarettes in 2014, according to CDC statistics. Spending on e-cigarette advertising also jumped, increasing to an estimated $115 million in 2014 from $6.4 million in 2011.

The CDC’s National Youth Tobacco Survey found that 68.9 percent of this age group saw e-cigarette ads from one or more media sources in 2014, most commonly in stores but also online, on television and in movies or magazines.

E-cigarettes contain cartridges that typically hold nicotine as well as other liquids and flavorings, and a heating element to create a vapor that the user inhales.

Many researchers believe e-cigarettes are less harmful than regular cigarettes, but the risks are still being studied.

Frieden said any tobacco use by young people could lead to brain damage, addiction and higher risk of becoming regular cigarette smokers.

“The use of e-cigarettes in kids appears increasingly likely to result in an increased risk of using regular cigarettes,” Frieden said.

Most states have passed laws banning the sale of e-cigarettes to minors, and the U.S. Food and Drug Administration’s proposal to regulate the products is under federal review.

Altria Group (MO) which owns three U.S. tobacco companies, is among e-cigarette sellers that have said they favor laws that prevent minors purchasing their products.