Now, researchers are looking into a potential new issue: lung problems caused by vaping.
Young people we talked to didn't seem to be worried about breathing in second-hand vapors.
"It really doesn't bug me," said Issai Rodriguez. "It doesn't bug me. They do their business. I do my business."
We asked Alyssa Aguilar if it bothers her when people vape around her, she said no, adding, "It doesn't smell like anything, and if it does, it smells good."
But those fruity and sweet vape flavors can mask nicotine, THC, heavy metals, and potentially harmful chemicals.
"The solvents they use and the little capsules have problems," said Dr. Tom Horowitz. "The bottom line is you're playing Russian roulette with your lungs."
Scientists are starting to look into the dangers of second hand vaping fumes.
Parents like Patricia Ortiz are very concerned about any aerosol vapors in the air.
"That's one of the reasons why I pick her up," said Ortiz. "I don't want her walking in that crowd because there are a lot that do it. So even if it's not in her hand, she's still breathing it in."
The long-term effects of vaping are not known, so doctors urge young people to stay away from areas where they might breathe in vaping fumes.
"You want to keep at least six feet away," said Dr. Horowitz. "You want to avoid going into rooms where there's a lot of vaping going on."
"They're putting this stuff in their lungs, turning back into a liquid or oil. It's leaving some of that behind in their lungs."
Robb Holladay tours the country talking about the dangers of vaping, and recently visited Kings Canyon Middle School.
Holladay says sometimes it can be difficult for kids to avoid the second-hand vapors.
"Most of the vaping in the school day takes place in the bathroom, in the stalls, so kids tell me, 'Robb, I go to the bathroom, and the vapor is everywhere.'"
It is a disturbing trend, and concerns over second-hand exposure are rising. A national youth tobacco survey showed a third of middle and high school students are exposed to vaping aerosols.
Telling friends they don't want to try a vape pen or asking them not to vape in their presence sometimes isn't easy for kids.
"Peer pressure is very difficult, and at the middle school level even more so," says Kings Canyon Middle School Principal, Edith Navarro.
Still, some teens want more medical proof the vapors are harmful before having those tough conversations.
"If it was actually proven that vaping is harmful, I would be a little more conscious of the effects," says Aguilar
But some of the medical experts we heard from insist, even passive exposure to vaping can pose a health risk.