Objective <p>This review assesses the respiratory effects of passive exposure to e-cigarette aerosols in adolescents, healthy adults, and individuals with pre-existing respiratory conditions.</p> Methods <p>We systematically searched for observational and experimental studies on secondhand e-cigarette aerosol (SHA) exposure. Outcomes included respiratory symptoms, pulmonary function, airway resistance or reactivity, inflammatory biomarkers, and environmental exposure metrics. Five studies met criteria: longitudinal cohorts, cross-sectional surveys, and controlled chamber experiments.</p> Results <p>Evidence suggests that SHA exposure is associated with adverse respiratory outcomes. In adolescents and young adults, household SHA increased bronchitic symptoms, wheeze, shortness of breath, and asthma outcomes. Risk rose with more frequent exposure. Controlled chamber studies in healthy non-smokers have found that 30&#xa0;min of passive exposure causes immediate sensory irritation (in the eyes, nose, and throat), increased airway resistance, and a decrease in exhaled nitric oxide. In COPD patients, short-term exposure affected surfactant protein-A, increased plasma inflammatory biomarkers, and caused throat irritation, with borderline lung function decline. Environmental monitoring confirmed the presence of ultrafine particles and volatile organic compounds during exposure.</p> Conclusion <p>SHA exposure is not benign. It can cause respiratory irritation, functional impairment, and inflammation in various populations. Effects are generally less pronounced than those of combustible cigarette smoke. Nonetheless, these findings support public health measures such as regulations restricting SHA exposure in public settings, especially to protect adolescents and vulnerable individuals. Long-term studies are still needed to determine chronic health consequences and guide evidence-based policy decisions.</p>