Effectiveness of Personal-Level Protective Measures Against Air Pollution on Respiratory Health: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.

Air pollution, particularly fine particulate matter (PM₂.₅), poses a significant global health risk, contributing to respiratory, and cardiovascular diseases. While personal-level interventions such as air purifiers and respirators are commonly used to reduce exposure, their effectiveness in improving clinical outcomes remains uncertain. This systematic review and meta-analysis evaluated the efficacy of such measures in reducing adverse respiratory and cardiovascular outcomes. A systematic search of PubMed, Embase, Scopus, and the Cochrane Library was conducted up to February 2025. Randomized controlled trials (RCTs) assessing the use of air purifiers or respirators in non-occupational settings were included. Meta-analyses were performed using fixed or random-effects models, and effect sizes were expressed as standardized mean differences (SMDs) with 95% confidence intervals (CIs). Certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) approach. Twenty-seven RCTs were included. Personal-level interventions significantly reduced indoor PM₂.₅ (SMD = -2.27; 95% CI: -2.98 to -1.55) and PM₁₀ (SMD = -3.87; 95% CI: -4.59 to -3.16) levels. However, no significant improvements were observed for forced expiratory volume in one second (FEV₁) (SMD = 0.04; 95% CI: -0.07 to 0.15), peak expiratory flow (PEF), forced vital capacity (FVC), respiratory symptoms, or blood pressure. Sensitivity analysis showed a significant reduction in FeNO (SMD = -0.16; 95% CI: -0.28 to -0.04). While effective in reducing particulate matter, personal-level interventions showed limited clinical benefits for respiratory or cardiovascular health.