From safer alternative to public health crisis: the unintended consequences of e-cigarettes.

Electronic cigarettes (e-cigarettes) were introduced as a harm-reduction alternative to combustible tobacco, offering nicotine delivery without combustion-related toxicants. However, their rapid global adoption has produced complex and unintended public health consequences. This editorial examines the evolving evidence on the safety, respiratory effects, and population-level impact of e-cigarettes. Early safety assumptions were largely based on ingestion toxicology rather than inhalation data, and many products entered the market without comprehensive preclinical or long-term human safety evaluation. Emerging epidemiological studies associate e-cigarette use with increased respiratory symptoms, while mechanistic research demonstrates airway inflammation, oxidative stress, and exposure to ultrafine particles, aldehydes, and metal contaminants. The 2019 outbreak of e-cigarette or vaping-associated lung injury lighted systemic regulatory vulnerabilities in the oversight of inhaled consumer products. In parallel, highly efficient nicotine delivery systems and youth-targeted product features have contributed to rising nicotine dependence among adolescents, shifting the public health burden. While some adult smokers may benefit from complete substitution, the net population effect remains uncertain when balanced against youth initiation and dual use. We argue that harm-reduction technologies require stronger regulatory frameworks, transparent risk communication, rigorous pre- and post-market evaluation, and youth-protective policies. A recalibrated, evidence-driven approach is essential to ensure that harm reduction reduces - rather than redistributes - health risk.