Indoor environmental health and asthma relief: findings from a longitudinal HEPA filter trial

Air purification is widely promoted to protect patients with allergic airway inflammation; however, evidence supporting its clinical benefits in asthma remains limited. This study aimed to evaluate the effectiveness of portable High-Efficiency Particulate Air (HEPA) H14 air cleaners on indoor air quality (IAQ) and asthma-related health outcomes using a randomized controlled trial design. A total of 100 adults with moderate-to-severe asthma were randomly assigned to either an active HEPA H14 air purifier group or a placebo group and followed for eight months, with assessments at baseline, 4 months, and 8 months. Indoor air pollutants (PM_2.5 and PM₁₀) and clinical outcomes, including Asthma Control Test (ACT) score, lung function, rescue inhaler use, and symptom-free days, were analyzed using intention-to-treat analysis. Compared with the placebo group, the active group demonstrated significant improvements in ACT score (β = 2.2, p = 0.004) and symptom-free days (β = 27.7%, P < 0.001), along with a marked reduction in PM₂.₅ levels (-29.6 µg/m³, P < 0.001). These findings indicate that improving IAQ through HEPA H14 filtration provides measurable clinical benefits and serves as an effective complementary intervention for asthma management.