Air purifiers range from highly effective (HEPA) to questionable (ionizers) to potentially harmful (ozone generators). Here is what the evidence supports for respiratory wellness.
True HEPA filters capture 99.97% of particles 0.3 microns or larger, including dust, pollen, pet dander and most mold spores. This is the technology with the strongest evidence for improving indoor air quality and respiratory comfort.
Ozone generators: produce ozone, a lung irritant. Ionizers: can produce small amounts of ozone and deposit particles on surfaces rather than removing them from the air.
HEPA purifier in the bedroom (where you spend 7 to 9 hours). Appropriately sized for the room (check CADR rating). Replace filters on schedule. This single intervention can meaningfully improve breathing comfort.