Air purifiers and humidifiers have different functions. Air purifiers are clean indoor air, but do nothing for indoor humidity levels. They remove dust and smoke from the air, as well as allergenic substances like animal dander and pollen. Humidifiers add water into the air, but do not clean it.

Ionizers are devices that disperse negatively or positively charged ions which attach to particles in the air. The particulate matter is then collected by the ionizer or attaches to nearby surfaces. Ionizers are typically sold as "air purifiers" that remove allergen or asthma-inducing particles from the air.

Many people have allergies to airborne dust, mold, and pollen. These tiny particles can accumulate in your home environment, potentially leading to health problems. At first glance, freestanding ionic air purifiers seem like a good deal: They’re affordable, quiet, and are said to clean particles from the air.