One in four American teens say they have been exposed to secondhand e-cigarette vapors, according to a new government study.

Secondhand smoke from e-cigarette vapors can contain harmful and potentially harmful substances, the researchers report in JAMA Pediatrics.

The 2015 National Youth Tobacco Survey found students exposed to secondhand tobacco smoke were much more likely to be exposed to secondhand e-cigarette vapors, HealthDay reports.

“To protect youth from both secondhand smoke and secondhand aerosol, smoke-free policies can be modernized to include e-cigarettes,” said lead researcher Teresa Wang of the Centers for Disease Control and Prevention. “These policies can maintain current standards for clean indoor air, reduce the potential for renormalizing tobacco product use, and prevent involuntary exposure to nicotine and other emissions from e-cigarettes.”