E-nicotine products, including e-cigarettes and vapes, have emerged as a global health concern, particularly among adolescents and young adults. The rapid rise in e-nicotine use among youth (1) occurs in the context of e-cigarette use rates that have overtaken that of combustible cigarettes in some countries (2). In addressing this significant global public health concern, this Research Topic's twelve articles provide an international perspective on youth e-nicotine use. The articles cover e-nicotine use starting with precursors of use (i.e., susceptibility) through risk and protective factors associated with e-nicotine use at personal (including brain structure), social network, and regulatory policy levels of analysis. The articles showcase the breadth and complexity of the challenges to be addressed in reducing e-nicotine related harms to health.

Prior to initiating e-cigarette use, the beliefs or expectancies that an individual has regarding the positive and negative effects of use (e.g., feeling relaxed or nauseous) robustly predict e-cigarette use (3), and indicate susceptibility (i.e., curiosity, intention, willingness to use) to e-cigarette use. Tarantino et al.'s analyses, reported in this Research Topic, found that adolescents' (aged 12–14) positive and negative e-cigarette expectancies were associated with perceived risk of harm from e-cigarette use, perceived peer disapproval and curiosity about e-cigarettes in the Adolescent Brain Cognitive Development Study conducted in the US (4). Examining susceptibility to e-cigarette use in older adolescents, James et al. found in their survey that over one-third of Oklahoma high-school students who had never used tobacco reported susceptibility to e-cigarette use. Among males in the survey, susceptibility was linked to low perceived e-cigarette harm. Furthermore, among females in the high school survey, psychological distress, lower academic performance, and sexual-minority identity predicted higher susceptibility and risk for e-cigarette use, suggesting important sex differences in risk that can inform interventions tailored to specific subgroups.

In the context of increasing worldwide prevalence of e-nicotine use, several contributions to this Research Topic investigated e-nicotine onset and prevalence across European, Middle Eastern countries, and Australia. Given the importance of preventing early initiation of e-nicotine use, Al-Naimi et al. conducted a retrospective survey study to identify factors related to early initiation (prior to the age of 18) of vaping. Their survey of 428 regular nicotine vapers (aged 18–60) residing in Middle Eastern countries found that males and adults living in Qatar had the greatest likelihood of early vaping initiation. Extending behavioral findings on early onset, Happer et al. reveal that earlier onset of regular nicotine use and greater craving and reinforcement symptomatology were associated with larger hippocampal volumes in adolescents and emerging adults. The hippocampus, rich in nicotinic acetylcholine receptors, is central to reinforcement learning and memory, suggesting that structural differences in this brain region may contribute to early addiction risk, emphasizing the importance of prevention and early intervention.

Two Research Topic studies, Hejda et al. and Kamoni et al. (5), found higher prevalence of e-nicotine use among males, relative to females. Specifically, male adolescents (aged 12–16) in Poland (Hejda et al.) and male Australian university students (aged 18–25) (5) were more likely to report e-nicotine use. These recent international findings add to the sex-related risk for e-cigarette use reported in adolescence (6). Importantly, since the prevalence of e-nicotine use in youth increases with age (1), Selya et al. observed that prevailing definitions of current e-nicotine use, often operationalized as any use within the past 30 days, may not correlate with clinically meaningful exposure during this developmental period. Their analysis recommends improvements to assessment of e-nicotine use by incorporating frequency, intensity, and persistence metrics to better distinguish transient experimentation from regular use that confers greater health risk.

Effectively reducing risk for e-nicotine use requires understanding the individual, interpersonal or social network, and community-level factors associated with youth e-nicotine use trajectories (6). At the individual level, for example, Kamoni et al. found that Australian university students who reported greater psychological distress, worse academic performance and alcohol use had higher risk for e-cigarette use (5). Similarly, the study by Lanza et al., which involved a regional sample of college students (aged 18–29) in the US, identified polysubstance use trajectories, such as nicotine/tobacco use and binge drinking. The co-occurrence of nicotine/tobacco use with other substance use shows how “syndemics” or co-occurring health conditions, which include overweight (Lanza et al.), can exacerbate the adverse health effects of e-nicotine/tobacco use on health.

Among the risk factors for e-nicotine use, family and peer nicotine/tobacco use robustly predict e-nicotine onset and use. For example, Hatz et al. demonstrate that peer and family nicotine/tobacco product use are the most consistent prospective predictors of emerging adult nicotine/ tobacco product initiation in a US regional sample, even after controlling for baseline use and concurrent cannabis or alcohol consumption. Notably, certain subgroups show protective resistance to peer influence. Specifically, Kozela et al.'s study revealed that women with low socioeconomic status residing in Poland reported being less affected by peer pressure against cigarette smoking and using heated tobacco products, indicating their overall risk for nicotine use may be less susceptible to social influence. Together, these findings align with conceptual models of substance use that emphasize the powerful role of social context and social influence in shaping nicotine use (7), and sex-differences in risk and protection that can inform tailored prevention efforts.

Another robust risk factor addressed in this Research Topic involves youth exposure to e-nicotine advertising, which has been previously linked to youth e-nicotine use (8). For example, Świątkowska et al. found in their sample of over 7,000 Polish adolescents and young adults, that over half reported exposure to e-nicotine advertisements. Specifically, seeing advertisements in club/pub/disco settings was significantly associated with reporting current e-cigarette use (Świątkowska et al.). Similarly, Wang et al. found in their online survey of 724 young adults (aged 18–30) in China that social media exposure to e-cigarettes/ vaping, perceived policy enforcement, and perceived risks and benefits of e-nicotine use were associated with vaping/e-cigarette use. These studies underscore how youth exposure to e-nicotine marketing, which focuses on the benefits of use, can shape youth perceptions of e-nicotine-related harms to health. In this regard, Hejda et al. found that nearly a third of youth (aged 12–16 years) surveyed in Poland reported that e-nicotine product use was less harmful than combustible cigarette use. These provocative findings emphasize the importance of disseminating accurate information regarding the health harms of e-nicotine use, and the need for effective nicotine/tobacco regulatory policy. To this point, Wang et al. (9) discuss the complexities and challenges in developing and enforcing effective tobacco/e-nicotine regulatory policy.

Across this Research Topic's twelve articles, converging evidence supports multifaceted assessment, and the need for multi-level prevention and intervention strategies: (1) refining measurement standards to capture experimental vs. persistent e-nicotine use; (2) targeting high-risk subgroups, especially those reporting psychosocial distress and social-media exposure and using tailored strength-based approaches to meet specific needs of subgroups and individuals; (3) addressing familial and peer normative influences; and (4) developing effective policy and interventions, particularly to account for the brain's heightened sensitivity to nicotine during adolescence and emerging adulthood (10). Collectively, findings from this Research Topic's articles call for harmonized epidemiologic definitions of nicotine and tobacco use and cross-disciplinary approaches to more effectively mitigate youth nicotine use worldwide.