HEPA air filtration for asthma and COPD: lessons from randomized controlled trials.

INTRODUCTION: People with asthma and chronic obstructive pulmonary disease (COPD) may experience worsening respiratory symptoms during high pollution events. High-Efficiency Particulate Air (HEPA) filtration removes fine particles and may reduce indoor exposure and respiratory morbidity. AREAS COVERED: We narratively synthesized randomized controlled trials (RCTs) of portable HEPA filtration in asthma and COPD. PubMed and Scopus were searched from inception to 5 May 2026, reference lists were updated on 10 June 2026. Trials consistently demonstrated substantial reductions in indoor PM2.5, but clinical effects were heterogeneous: several asthma trials reported improvements in symptoms, peak flow and/or quality of life, particularly in highly symptomatic or higher‑exposure subgroups, whereas most spirometric endpoints showed small or no change. Evidence for benefit in people with COPD was limited but promising. Key methodological limitations across trials included short follow‑up periods, lack of adult studies, information on device specifications, adherence measurements, economic evaluations, and under‑representation of low‑resource settings. EXPERT OPINION: HEPA filtration warrants further evaluation in adequately powered, pragmatic RCTs with standardized device specification reporting, longer follow‑up, adherence support, prespecified primary outcomes and cost‑effectiveness analyses. Trials should include diverse populations and assess high‑exposure periods, and public clean‑air shelters to inform equitable policy for protecting vulnerable populations.