An ozone generator produces ozone that attacks the source of odor-causing gases through a process called oxidation and permanently removes odor. This is very different from a negative ion generator, or ionizer, whose main purpose is to reduce particles such as dust and pollen that float in airspace. Ozone, a lung irritant, is produced indirectly by ion generators and some other electronic air filters and directly by ozone generators. While indirect ozone production is a matter of concern, there is even greater concern with the direct and deliberate introduction of a lung irritant into indoor air.
Despite some vendors' claims, there is no difference between ozone in outdoor smog and ozone produced by these devices. Under certain conditions of use, ion generators and other air purifiers that generate ozone can produce levels of this lung irritant significantly above levels considered harmful to human health. A small percentage of air purifiers claiming a health benefit may be regulated by the FDA as a medical device. The Food and Drug Administration has set a limit of 0.05 parts per million ozone for medical devices.
Although ozone can be used to reduce odors and pollutants in unoccupied spaces (such as removing smoke odors from homes involved in fires), the levels needed to achieve this are above those generally believed to be safe for humans. If you are wondering about the differences between an air ionizer and the typical HEPA filter on the market, below is a quick comparison table showing the differences between these products. Since the conflicting data associated with the ionizer remains persistent, I usually keep my ionizer option turned off. If you've come this far and digested all the information about air ionizers (whether they're marketed as ionic air purifiers or ionizers), you've probably already realized that most people shouldn't buy an air purifier with an ionizing function.
Ionizer air purifiers are generally safe because ionizers aren't energized enough to be harmful to you. These ionizers turn on for 8 hours every day, and I have a Therapure TPP300D with UV+ ionizer that turns on for 8 hours in my living room. Air ionizers are designed to help provide cleaner air and they do so through the use of ionized particles.