The number of youths in the U.S. who used e-cigarettes tripled from 2011 to 2013, sparking concerns over a new generation of smokers, the Associated Press reported on Monday.

Roughly 79,000 middle and high school students tried e-cigarettes in 2011, compared to more than 263,000 in 2013, according to data from National Youth Tobacco Studies. That was a threefold increase over the number that tried the electronic smoking devices in 2011, according to the journal Nicotine and Tobacco Research.

Lead author Rebecca Bunnell, associate director for science in the CDC's Office on Smoking and health, told the AP that an increase in young e-cigarette smokers should be a concern for parents and public health workers. 

"Especially since youth e-cigarette users were nearly twice as likely to have intentions to smoke conventional cigarettes compared with youth who had never tried e-cigarettes," she told the AP.

The study also found that 44 percent of youths who had tried e-cigarettes said they intended to smoke regular paper cigarettes within the next year.

Comparatively, among those that had never tried e-cigarettes, only 22 percent said they intended to try conventional cigarettes.

E-cigarettes are cigarette-shaped devices that heat flavored nicotine liquid into vapor that is inhaled by users, but doesn't produce smoke, according to MSN News. The vapor is exhaled by the smoker and it quickly evaporates into the air.

The devices aren't regulated and may be marketed to minors. Sweet flavors like candy and fruit make them an additional risk to youth, experts say.

The American Heart Association has pressed for them to be subject to the same regulations as cigarettes and wants to see them banned from being sold to minors.

The FDA has proposed some regulations, but they have not been implemented yet.