Ionic air purifiers generate ozone, a respiratory irritant that can worsen asthma and emphysema and may compromise the ability to fight off respiratory illnesses. Consumer Reports advises against using any air purifier that generates ozone even if it is otherwise effective.
The best air purifiers use high energy particle air filters to remove pollen, pet dander, particles from cigarette smoke and some kinds of dust from indoor air. Both whole-house and portable systems can remove contaminants effectively but are generally ineffective at removing odors. Before buying an air purifier, see if basic measures to reduce indoor air pollution can maintain acceptable air quality. These include frequent vacuuming, banning indoor smoking, keeping indoor fires and use of candles to a minimum, storing volatile chemicals outside the house, ensuring proper venting of appliances that burn gas or wood and using exhaust fans in kitchens, laundry areas and bathrooms.