The best air purifiers are sometimes pitched as the best way to improve the air quality in your home. But their usefulness is often overblown — and some air purifiers, such as those with ionizing functions that produce ozone, may actually be detrimental to your health.

According to the Environmental Protection Agency, the best way to improve indoor air quality is to get rid of the source of pollutants and ventilate your interior spaces with clean outdoor air. While air purifiers can reduce airborne pollutants, they cannot eliminate them. They also can’t clear the dust, dander and other particles that have already settled on surfaces around your home.