The study, published on July 11 in the journal Pediatrics, followed five groups of high schoolers who graduated in 1995, 1998, 2001, 2004 and 2014. We attempted to contact all never-smoking e-cigarette users (n = 213) and a randomly selected frequency matched sample of never-smoking, never e-cigarette users (n = 213) from among all never-smoking never e-cigarette users in the cohort at initial evaluation; never-users were frequency matched to e-cigarette users by gender, ethnicity, and grade (11 or 12). has done tests on these vaping products that supposedly do and do not contain nicotine, and what is advertised is really not what’s in the product,” Dr. Winickoff said. What This Study Adds: The high prevalence of combined e-cigarette or cigarette use in 2014, compared with historical Southern California smoking prevalence, suggests that e-cigarette use is occurring in adolescents who would not otherwise have used tobacco products. Data from the National Youth Tobacco Survey (NYTS), a nationally representative cross-sectional survey of adolescents in the United States, show that current (past 30-day) use of e-cigarettes increased exponentially from 1.1% in 2011 to 16.0% in 2015 among high school students.2–6 While the prevalence of e-cigarette use is increasing, cigarette use is generally declining among adolescents; in the NYTS, current cigarette use among high school students fell from 15.8% in 2011 to 9.2% in 2014,2,3,5,6 continuing the decline in prevalence of cigarette use among adolescents from its most recent peak in the mid-1990s when the prevalence of current smoking reached 35%.7 Of note, the prevalence of cigarette smoking did not continue to decline from 2014 (9.2%) to 2015 (9.3%).6 In 2014, current use of e-cigarettes surpassed current cigarette use for the first time in several national studies (including the NYTS2 and the Monitoring the Future Study8), as well as in a number of local and state-level studies,9–11 including our study of Southern California adolescents.12 
 
 There are multiple interpretations of recent trends in e-cigarette and cigarette use among adolescents. Photo 
 
 Many teenagers who never would have smoked cigarettes are now “vaping” with flavored e-cigarettes, leading to a new generation using nicotine at rates not seen since the 1990s, a new study suggests. Alternatively, e-cigarettes may be recruiting new users who otherwise would not have initiated cigarette use (or perhaps any other tobacco product) if e-cigarettes were not available. Recent data from the 2015 NYTS found a small, nonsignificant increase in the use of any tobacco product from 2013 to 2015 (from 22.9% to 25.3%).2,6 The increase in overall tobacco product use appears to be largely driven by increases in e-cigarette and hookah use in 2013 and 2014, and continued increases in e-cigarette use in 2015, along with no decline in cigarette smoking from 2014 to 2015.2,3 Although these data provide insight into trends over the preceding 3 years, adolescent tobacco use has declined for >20 years.7 The impact of e-cigarettes on adolescent tobacco use trends that have evolved over longer periods is unknown. Questionnaires were completed with study staff supervision between January 2014 and June 2014, when use of e-cigarettes was first assessed in the cohort.6,18 To maximize efficiency in the design of the prospective follow-up study to evaluate the risk of cigarette and other combustible tobacco product initiation associated with e-cigarette use, we used an exposure frequency-matched cohort study design in which we contacted never-smoking e-cigarette users and a sample of never-smoking never e-cigarette users to complete a follow-up questionnaire (Fig 1). Written parental informed consent and student assent were obtained for all CHS participants before data collection in 2014. Estimates were based on 39 (27.1%) initiators and 18 (12.5%) past 30-day cigarette users among e-cigarette users at baseline, compared with 12 (7.9%) initiators and 4 (2.6%) past 30-day cigarette users among never e-cigarette users at baseline; 2 participants reported initiation of smoking but did not report the number of days smoked in the past 30 days (results not tabulated). In 2014, smoking history was assessed in Cohort E participants (in grades 11 and 12) using the same question as in Cohorts A through D, along with 2 additional questions that asked about the age at which each participant had first used a cigarette (“even 1 or 2 puffs”) and the number of days smoked in the past 30 days. Measures Tobacco and Alternative Tobacco Product Use At each survey, participants were asked whether they had ever tried e-cigarettes, cigarettes, cigars, pipes, or hookah and the number of days each product was used in the past 30 days.6 Participants who had “never tried” a product (not “even 1 or 2 puffs”) were classified as “never users.” Those reporting an age at first use of each tobacco product were classified as “ever users” of that product. Sociodemographic Characteristics Self-administered questionnaires completed by parents of participants18 were used to assess gender, ethnicity (Hispanic, non-Hispanic white, other), and parental education (highest level of education of either parent; <12th grade, high school diploma or general equivalency diploma, some college, college degree, some graduate school or higher). Results did not differ appreciably after additional adjustment for social environment characteristics at initial evaluation (whether others in the home smoked, number of friends who smoked, friends’ attitudes toward smoking), age at initial evaluation, age at follow-up, or time in months from initial evaluation to follow-up (results not shown). However, the risk of smoking associated with e-cigarette use was even higher among participants who reported no intention to smoke at initial assessment than among the group of adolescents who indicated they were likely to begin smoking. This substantially increased combined prevalence of cigarette smoking or e-cigarette use in 2014, compared with smoking rates a decade earlier, when e-cigarettes were not available, suggests that e-cigarettes are not used only by adolescents who would otherwise be smoking cigarettes. No notable differences in gender, ethnicity, grade, or susceptibility to cigarette use were observed between retained participants and those lost to follow up. The initial data addressing this question came from several cross-sectional studies that examined the association between e-cigarette use and self-reported intention to use cigarettes among adolescents with no previous history of cigarette use, using validated survey measures.7–13 E-cigarette users, representing several age groups and geographic locations, had 2 to 4 times the odds of indicating an intention to use cigarettes as never users,7,8 results consistent with those we reported in the CHS.9 To date there have been 3 reports from prospective cohort studies examining the relationship between e-cigarette use and subsequent initiation of combustible cigarette use in adolescence, including a study of 9th-grade students (mean age 14.1),14 a second study of 9th and 10th-grade students (mean age 14.7),15 and another small study of 16- to 26-year-olds, with few never-smoking e-cigarette users at baseline that was not able to examine associations within specific developmental periods in this age range.16 All studies found that e-cigarette use was associated with elevated risk of initiation of combustible cigarettes. Data on e-cigarette use were collected in 11th and 12th grade (mean age = 17.4); follow-up data on tobacco product use were collected an average of 16 months later from never-smoking e-cigarette users at initial evaluation (n = 146) and from a sample of never-smoking, never e-cigarette users (n = 152) frequency matched to e-cigarette users on gender, ethnicity, and grade. In sensitivity analyses, models evaluating the risk of initiation of cigarettes were restricted to nonusers of any combustible tobacco product at initial evaluation (cigarettes, cigars, hookah, pipes). E-cigarettes have gained popularity in recent years, in part because of availability in a wide variety of flavorings21 that may be appealing to adolescents and young adults,22 the perception that e-cigarettes are less harmful than smoking,23 absence or poor enforcement of regulations on indoor use,24 and the recent popularity of product-specific venues that encourage use of these products in social situations, such as vape shops.25 Such characteristics of e-cigarettes may be recruiting new users who are deterred from initiating cigarettes because of concerns about the health hazards of smoking and social stigmatization of cigarette use.7 There is concern that the increasing prevalence of e-cigarette use could even lead to initiation of smoking among previously nonsmoking adolescent e-cigarette users in what has been described as a “gateway effect,” either as a result of social normalization of alternative product use and smoking behaviors more generally, leading to renormalization of smoking or by directly increasing use of cigarettes through establishment of reward seeking behaviors (eg, nicotine dependence).26–30 Although our results demonstrated a decline in cigarette use in the past decade, we also have observed a markedly increased likelihood of intention to use cigarettes31 among e-cigarette users in the CHS in 2014 who had never smoked, results which are consistent with 2 recent studies examining the association of e-cigarette use with susceptibility to smoking,28,30 and recent longitudinal studies that have found that never-smoking e-cigarette users were more likely to report use of cigarettes a year later than never e-cigarette users.32–34 The use of e-cigarettes by nonsmoking adolescents poses several potential public health problems. First, use of e-cigarettes containing nicotine may directly contribute to nicotine dependence in late adolescence or early adulthood, putting adolescents at risk for lifelong nicotine dependence.35,36 Use of e-cigarettes, even without nicotine, may normalize tobacco product use behaviors more generally, which could then lead to increased rates of addiction via use of other nicotine-containing products, including cigarettes and other harmful combustible tobacco products.35–37 Second, in addition to lifelong problems associated with nicotine dependence, exposure to nicotine in adolescence adversely affects cognitive function and development.19 There is also evidence that e-cigarettes may generate aldehydes and other toxic chemicals and that flavoring additives may induce adverse respiratory health effects in e-cigarette users.38 Although the adverse health effects of e-cigarettes may be less than those of cigarettes, the long-term consequences of e-cigarette use are not known because these products have been on the market for less than a decade. Conclusions Longitudinal data on emerging adolescent tobacco and alternative tobacco product use, including detailed information on topography of e-cigarette use and dose of nicotine, are needed to understand the role of e-cigarettes in nicotine addiction and whether e-cigarette users who have not used combustible cigarettes will, in the future, continue using e-cigarettes only, quit using tobacco products altogether, or progress to combustible cigarette users or dual users of both products.
– With the debut of vaping in the US in 2007, there was hope that teens who smoked would replace old-school cigarettes with e-cigarettes, curbing tobacco use. But a new USC study in the journal Pediatrics has found teens who never would have smoked regular cigarettes are experimenting with vaping. Another USC study finds older teens who try vaping are six times more likely to try a tobacco-filled cigarette than non-vapers, per a press release. "E-cigarettes may be recruiting a new group of kids to tobacco use," says Jessica Barrington-Trimis, lead author of both studies. While e-cigs may seem safer than tobacco, if they come pumped with nicotine (some don't), kids can get addicted. The New York Times notes chemicals in the vaping liquid may be harmful; WebMD adds long-term effects are unknown. Using participants from USC's Children's Health Study, scientists followed 5,490 teens who graduated high school in select years between 1995 and 2015, asking them via questionnaire about their tobacco use. It's true that rates among Southern California teens who said they had smoked over the past 30 days fell significantly from 1995 to 2004 (19% to 9%), and slightly more in the decade after that (a bit less than 8% by 2014). But when teens were asked to include e-cigarettes in their assessments, the smoking rate jumped back up to 14% in 2014. And that's got scientists worried, especially with the prevalence of e-cigarettes that come in kid-friendly flavors such as cotton candy. "E-cigarettes may be safer than regular cigarettes for adults who are transitioning from smoking to vaping, but for youth who have never used any other tobacco products, nicotine experimentation could become nicotine addiction," Barrington-Trimis says.