Buying an air purifier can feel like being sold a bill of goods: It has a hefty price tag and does a job you can't see, feel, or taste. Should you get one?

Studies done by the Association of Home Appliance Manufacturers (AHAM) show that air cleaners safely remove up to 99.7 percent of allergens and pollutants (they were inconclusive, however, about any specific health benefits). The units that work best against odors, as opposed to just allergens and pollutants, have pleated HEPA (high-efficiency particulate air) filters plus a supplemental filter of activated carbon or charcoal. The Environmental Protection Agency (EPA) cautions consumers against models that advertise the use of trace amounts of ozone, which gives off a nice scent but can be irritating to the lungs and throat.

AHAM has set up a certification program called the Clean Air Delivery Rate (www.cadr.org) and evaluated more than 170 portable air cleaners. (Blueair units rated high; www.blueair.com.) When you shop, know the square footage of the room that will house the unit (poorly ventilated spaces are a good place to start) so you know which one to buy. Prices range from just under $100 to upwards of $1,000. If you don't have space to spare, try the new lightbulbs coated with titanium dioxide, such as the O-ZoneLite ($40, www.ozonelite.com; lasts about two years). They act as mini HEPA filters, eliminating airborne bacteria that may cause odors.