Respiratory Effects of Electronic Cigarettes and Emerging Tobacco Products: A Review

Abstract

Objective: To critically synthesize current evidence on aerosol composition, respiratory mechanisms, clinical outcomes, e-cigarette or vaping product use-associated lung injury (EVALI), and smoking cessation. Methods: PubMed/MEDLINE and the Cochrane Library were searched with prespecified search strings for publications dated January 1, 2015 through August 5, 2026. Official World Health Organization and US Centers for Disease Control and Prevention documents and reference-list searches supplemented database retrieval. Eligible original studies, systematic reviews, and authoritative guidance documents were selected purposively and synthesized thematically. Results: Electronic cigarette and heated-tobacco emissions may contain nicotine, ultrafine particles, carbonyls, volatile organic compounds, metals, and thermal degradation products. Experimental studies support epithelial barrier disruption, oxidative stress, impaired mucociliary function, altered host defense, and inflammation. Observational human evidence links use with cough, wheeze, and bronchitic symptoms, although dual use, residual confounding, rapidly changing devices, and short follow-up limit causal inference. EVALI is an acute lung-injury syndrome identified during the 2019 US outbreak and strongly associated with informal THC products and vitamin E acetate. Nicotine e-cigarettes may improve cessation in selected adults, but long-term respiratory safety remains uncertain. Conclusion: These products should not be considered harmless. Clinical care should document each product separately, prioritize complete cessation of combustible tobacco and inhaled nicotine/tobacco products, use licensed cessation treatments when indicated, and protect never-smokers, adolescents, and pregnant people.