Fewer U.S. teens are smoking regular cigarettes, but more are using e-cigarettes, according to the Centers for Disease Control and Prevention (CDC).

Last year, 11 percent of high school students said they smoked a regular cigarette in the last 30 days, while 24 percent said they used e-cigarettes in the past month. The survey found 45 percent of teens said they had tried an e-cigarette at least once.

Current cigarette use has decreased significantly. In 1991, 28 percent of high school students said they smoked cigarettes. The findings come from the National Youth Risk and Behavior Survey, which included more than 15,000 high school students.

“Current cigarette smoking is at an all-time low, which is great news. However, it’s troubling to see that students are engaging in new risk behaviors, such as using e-cigarettes,” CDC Director Tom Frieden, MD, MPH, said in a news release. “We must continue to invest in programs that help reduce all forms of tobacco use, including e-cigarettes, among youth.”

Patricia Folan, Director of the Center for Tobacco Control at Northwell Health in Great Neck, New York, told HealthDay a number of factors have led to the decline in smoking among teens. These include “environmental tobacco bans, increased taxes on cigarettes, anti-tobacco media campaigns, as well as the removal of point-of-sale tobacco advertising from stores,” she said.

E-cigarettes may have a harmful health effect on teens, Folan said. “These products contain nicotine, an addictive substance, which has a powerful and detrimental effect on the developing brain of youth and young adults,” she noted.

The survey also found fewer high school students reported illicit use of a prescription drug one or more times. In 2009, 20 percent of teens said they had taken prescription drugs without a doctor’s prescription, compared with 17 percent in 2015.