Is your air cleaner hazardous to your health?

If you're shopping for an air cleaner, you'll find two main types. The best kind simply filter bad stuff (pet dander, dust, pollen, smoke, etc.) out of the air you breathe. But other air purifiers try to "clean" the air by pumping out ozone -- a chemical that's actually helpful as long as it lingers in Earth's stratosphere, screening out the sun's damaging ultraviolet (UV) rays, and that turns dangerous when it descends into the air we breathe. ("Good up high, bad nearby," as the U.S Environmental Protection Agency says.) These so-called "air purifiers" can actually pollute your home's air and trigger breathing problems, experts warn in our latest report on air purifiers.

Ozone irritates the lungs and throat and can worsen asthma, weaken your body's ability to fight infections, and cause other health problems -- even in healthy people, the EPA warns. In fact, long-term exposure to even low levels of ozone can kill you, according to a study published in The New England Journal of Medicine.

The EPA cautions against using air cleaners that produce ozone. So does Good Housekeeping magazine. "Don't buy them," is Good Housekeeping's advice on ozone-generating air purifiers. Adding: "We feel so strongly that these products are hazardous to your health that we will not allow them to apply for use of the Good Housekeeping Seal or advertise in Good Housekeeping." If you already have one, "stop using it and cut the cord before you discard it so no one else can use it either." ConsumerReports.org refuses to recommend or even test them. And as of October 2010, the state of California has banned the sale of home-use air cleaners that produce more than 50 parts per billion of ozone.

So, how can you tell whether your air purifier is safe? Unfortunately, it can be tricky. If you see the word "ionic" or "electrostatic" on your air cleaner, it's probably dribbling out small amounts of ozone as a by-product. Also look for code words like "pure air," "energized oxygen," "saturated oxygen" or "trivalent oxygen" -- all of which can really mean ozone. You can also test for ozone with a free kit from the not-for-profit International Association of Air Cleaner Manufacturers (IAACM). To be on the safe side, avoid such electrostatic air cleaners, ConsumerReports.org advises: "We now believe that air purifiers that emit even small amounts of ozone (less than 50 parts per billion) are not your best choice."

To avoid the whole ozone problem, simply choose an air cleaner that uses filters only (usually HEPA and/or carbon filters). Experts say these do the best job of cleaning the air, anyway, and without any potentially dangerous side effects. All of the Best Reviewed air cleaners in our latest report produce zero ozone, from the elite IQAir HealthPro Plus (*Est. $900) to the more affordable Austin Air HealthMate (*Est. $490) and Honeywell Enviracaire 50250-N (*Est. $195) to the inexpensive 3M Filtrete 2200 Elite Allergen Reduction Filter (*Est. $23), a disposable filter that slips into your forced-air heating or cooling system.