A study published online in JAMA Pediatrics showed that the higher the nicotine concentration in the e-cigarettes high school students used, the greater the chance those teens increased the frequency and intensity of combustible cigarettes or vaping in the future.

Researchers’ findings are based on the results of following 181 students, split almost evenly between boys and girls, from 10 high schools in the Los Angeles area. The students were surveyed during the spring of 10th grade and participated in a follow-up in the fall of 11th grade.

At the baseline evaluation, students reported using e-cigarettes within the past month and they reported the nicotine concentration levels they used as being none, low (1–5 mg/mL), medium (6–17 mg/mL) or high (equal to or greater than 18 mg/mL). Students also reported how frequently they used combustible cigarettes and e-cigarettes in the past month, and reported the daily intensity of the smoking and vaping, including the number of cigarettes per day, as well as the number of vaping episodes per day and the number of puffs per vaping episode.