The Evolving Landscape of Electronic Cigarettes: A systematic review of recent evidence

Abstract Smoking continues to be a burden to economies and healthcare systems across the world. One proposed solution to the problem has been e-cigarettes; however, as a relatively new product in the market, little is known about their potential health impacts. Furthermore, e-cigarettes continue to evolve at a rapid rate, making it necessary to regularly review and synthesize available studies. Whilst e-cigarettes are marketed as a smoking cessation tool by some manufacturers, the reality is that many non-smokers, including youth, are using them. In this review we focus on two major demographics - smokers and non-smokers, and evaluate the most recent data (2018-2019) regarding the potential health effects of e-cigarettes. We assessed peer-reviewed studies on health impacts of e-cigarettes with particular focus on common questions asked by policy makers, clinicians, and scientists: 1. What are the effects of e-cigarettes compared with air/not-smoking?; 2. Is there any direct evidence of harm or benefit to humans?; 3. Is there a risk from second-hand exposure?; 4. What are the risks and/or benefits of e-cigarettes compared with tobacco cigarette use?; 5. Are there risks or benefits to specific populations – people with COPD or asthma, and pregnant women (and their offspring)?; 6. What are the effects of flavoring chemicals?; 7. What are the effects of including nicotine in e-liquids?; 8. How often is nicotine-level labelling incorrect? and 9. What are the risks when e-cigarettes explode?