As e-cigarette use soars in high schools across America, new research shows many people don’t understand the amount of addictive nicotine they’re inhaling with every puff. In a new survey, many teens said they regularly used e-cigarettes, but swore they only vaped nicotine-free products.

However, urine tests for a “marker” of nicotine use came up positive 40 percent of the time in this same group of vapers, the researchers reported. “Many of our participants were unaware of the nicotine content of the e-cigarette products they were using,” concluded a team led by Dr. Rachel Boykan, a pediatrics researcher at Stony Brook University in Stony Brook, N.Y.

That could mean even more lifelong nicotine addictions arising in the young, including many who already believe vaping to be “harmless” compared to traditional smoking, experts said. Patricia Folan directs the Center for Tobacco Control at Northwell Health in Great Neck, N.Y. She said, “Other studies have revealed that one of the main reasons adolescents use e-cigarettes is that they perceive them to be less harmful than combustible cigarettes — without full knowledge of their actual contents.”

But the new study “shows that many of the participating youth were unaware of the nicotine content in their vaping devices,” Folan said. The study findings were published online April 22 in the journal Pediatrics. As Boykan’s group noted, about one in five high school students now say they’ve used an e-cigarette at least once over the past month, and in just the 12 months between 2017 and 2018, teen vaping rates soared 78 percent.

But do young people even understand the addictive dangers of nicotine-laden vaping products such as Juul vape “pods”? Overall, the survey participants were largely honest about their use of tobacco, e-cigarettes, and marijuana: Only about 2 percent who said they didn’t use those substances later were found to have evidence of tobacco, nicotine or pot in their urine samples.