A simple air filter could cut indoor pollution in half and even lower your blood pressure if it’s already on the high side. In a new study, researchers enrolled adults living within 200 meters of a highway. Each person had one month with real HEPA filters in their bedroom and living room and one month with sham filters (same look and sound, no filter). Indoor particulate matter levels dropped by ~50% with HEPA filters and particle counts fell from ~6,300 to ~4,700 particles/cm³. Overall, there was no significant group-wide effect on blood pressure (only a small 0.5 mmHg reduction compared to the sham condition), but among people with systolic BP ≥120 mmHg, HEPA use lowered systolic BP by ~3 mmHg. If you live near heavy traffic, especially with higher baseline blood pressure, using HEPA filtration indoors can significantly reduce particle pollution and may modestly lower your systolic BP.