The rate of teens who use nicotine, through e-cigarettes or tobacco cigarettes, is increasing, a new study finds. Researchers say many teens who never would have smoked traditional cigarettes are now using e-cigarettes.

The study included data from 5,490 California high school seniors who graduated between 1995 and 2014. It found about 14 percent of high school seniors in Southern California in 2014 said they had smoked or vaped in the past month. About 8 percent of seniors said they had smoked tobacco in the past 30 days.

Nicotine use has not been so high among teens since 1995, when 19 percent of high school seniors said they smoked, The New York Times reports. The study appears in the journal Pediatrics.

“If teenagers who vape are using e-cigarettes instead of cigarettes, we would have expected to see the decline in smoking rates continue through 2014,” lead author Jessica Barrington-Trimis of the USC Keck School of Medicine said in a news release. “But what we’ve seen is a downward trend in cigarette use from 1995 to 2004 but no further decrease in cigarette smoking rates in 2014. The combined e-cigarette and cigarette use in 2014 far exceeded what we would have expected if teens were simply substituting cigarettes with e-cigarettes.”