With electronic cigarettes often touted as a safer alternative to traditional cigarettes, another study is casting doubt on that assertion.

In a study published this month in Pediatrics, researchers found that while e-cigarette vapor may be less hazardous than combustible cigarette smoke, it still contains volatile organic compounds identified as carcinogenic. More worrisome is that the study focused on adolescent e-cigarette users. Nationwide, the Centers for Disease Control and Prevention reports that e-cigarette use among middle and high school students tripled between 2013 and 2014, from 4.5 percent to 13.4 percent or from about 600,000 to 2 million students. More recent CDC data found that in 2016, 11 of every 100 high school students, or more than 11 percent, reported e-cigarette use in the last 30 days.

“To our knowledge, there are not data on toxicant exposure in adolescent e-cigarette users,” researchers wrote in the new study. “However, there is great concern because exposure to toxicants during adolescence may result in greater harm than exposure in adulthood, given vulnerability to the acute and chronic effects of toxicants in general and from their cumulative exposure if started early.”

To conduct the Pediatrics study, researchers divided about 100 adolescents into three categories: e-cigarette-only users; e-cigarette and regular cigarette users — also referred to in the study as dual users; and those who never used either. Saliva and urine samples were collected within 24 hours of last e-cigarette use. With an average study participant age of about 16 years old, researchers found that urine levels of benzene, ethylene oxide, acrylonitrile, acrolein and acrylamide were significantly higher in dual users compared to those who only used e-cigarettes. However, excretion of metabolites of acrylonitrile, acrolein, propylene oxide, acrylamide and crotonaldehyde were significantly higher in e-cigarette-only users than in nonusers.

For example, excretion of metabolites of acrylonitrile — widely used in the manufacture of plastics and adhesives and that the U.S. Environmental Protection Agency has designated as a probable carcinogen — was 341 percent higher in e-cigarette-only users than in nonusers and 327 percent lower than in dual users. Metabolites of acrolein — sometimes used as a pesticide and with unknown carcinogenic effects — was 20 percent higher in e-cigarette-only users than nonusers and 11 percent lower than for dual users.

Propylene oxide — a component in polyurethane foams and classified as a probable carcinogen — was 51 percent higher in teens only using e-cigarettes than in nonusers. Metabolites of acrylamide — an industrial chemical that the National Cancer Institute says is “reasonably anticipated” to be a human carcinogen — was 30 percent higher in e-cigarette-only users than in nonusers. And metabolites of crotonaldehyde — used to make sorbic acid and that EPA considers a possible carcinogen — were 20 percent higher in e-cigarette-only users than in nonusers. Fruit-flavored e-cigarettes were also associated with higher levels of acrylonitrile.

Overall, teen e-cigarette users had levels of the five volatile organic compounds that were three times greater than nonusers. Levels of the toxicants in dual users were up to three times higher than among teens only smoking e-cigarettes.

“Although e-cigarette vapor may be less dangerous than combustible cigarettes, with lower overall exposure to (volatile organic compound) toxicants, with our findings, we challenge the idea that e-cigarette vapor is safe,” the study concluded. “Consequently, as with traditional cigarettes, messaging to teenagers must include warnings about the potential risk from toxic exposure to carcinogenic compounds generated by these products.”

For a copy of the new e-cigarette study, visit Pediatrics.