INTRODUCTIONThis study was conducted to explore the characteristics and risk factors of e-cigarette use in adolescents, aiming for tobacco control and reducing e-cigarette use in this population.METHODSUsing 1:1 matching, 88 students from three vocational high schools in Shanghai were recruited to conduct a case (using e-cigarettes) - control (not using e-cigarettes) study. Group interviews and questionnaire surveys were used for this qualitative and quantitative mixed-methods study. The keywords were extracted from the interview data and analyzed by the Colaizzi seven-step method.RESULTSThe characteristics of adolescents’ use of e-cigarettes include young age at first use, consumption of a large amount, as well as smoking in discrete locations in order to hide from adults. The reasons for using e-cigarettes include curiosity and wanting to replace traditional cigarettes. The risk factors of using e-cigarettes include insufficient understanding of the harm of e-cigarettes at the individual level (The positive outcome expectancy points: Z= -3.746, p<0.001; The negative outcome expectancy points: Z= -3.882, p<0.001), peer influence at the interpersonal level (χ2=6.510, p<0.01), and the influence of social and environmental factors such as e-cigarette sales in the stores and WeChat Moments (p<0.05 for all associations).CONCLUSIONSHaving friends who use e-cigarettes, curiosity and sales exposure about e-cigarettes are important factors affecting the use of e-cigarettes by adolescents. It is necessary to strengthen the publicity of the potential hazards of e-cigarettes and to reduce overall usage by improving relevant laws and regulations.