WASHINGTON (AFP) - The number of young Americans using e-cigarettes grew by 1.5 million in 2018, undermining years of progress in reducing youth smoking, health authorities said Monday (Feb 11).

Some 3.6 million middle and high school students were current users of vaping products, up from 2.1 million the year before, while the number of cigarette smokers and consumption of other tobacco products remained stable, according to the report by the Centers for Disease Control and Prevention (CDC).

A current user is defined as a person who has used a product in the past 30 days.

"The skyrocketing growth of young people's e-cigarette use over the past year threatens to erase progress made in reducing youth tobacco use," said CDC Director Robert Redfield.

"It's putting a new generation at risk for nicotine addiction."

Authorities have tightened regulations, with market leader Juul in particular coming under particular scrutiny.

"All policy options are on the table," warned Mitch Zeller, Director of the Center for Tobacco Products at the Food and Drug Administration, which regulates vaping and in November restricted the sale of certain flavors such as fruit and chewing-gum.

Vaping began to take off among young Americans in the 2010s, and overtook cigarette smoking in 2014.

While the number of middle and high school cigarette smokers has been falling steadily since 2011, the number of vapers in that group has increased dramatically, from 1.5 percent then to 20.8 in 2018.

The survey estimates 4.9 percent of college students vape.

The US categorises e-cigarettes as tobacco products, a definition not shared by all countries.