You'll find them in the dining room, living room, and even in the bathroom.

But did you know some of the same purifiers designed to clean the air, actually release a dangerous pollution into our homes.

They generate ozone, which can be especially irritating to people with asthma and other lung problems -- the same people who often buy these products to improve their health.

Ozone is the most harmful component of smog.

The California Department of Health Services also recommends you read between the lines on the product labels.

Often manufacturers refer to ozone as "activated oxygen" and "nature's air purifier" to suggest that it is safe.

Margo Sidener from the American Lung Association says, "Air filters work in a variety of different ways. Some actually emit ozone, which can be a very strong lung irritant."

It is the same stuff that triggers "Spare The Air" days around here, and sometimes sends people to the hospital with breathing trouble.

Kaiser pulmonologist Dr. Thomas Dailey says, "Ozone in air pollution has definitively been associated with causing breathing problems in children, and in patients with asthma and emphysema."

The Environmental Protection Agency says even low amounts of ozone can cause chest pain, coughing and shortness of breath.

So how do you know if your purifier emits ozone?

It is important to look at both the inside and outside label.

For example, one model clearly tells consumers on the outside of the box that the purifier produces low levels of ozone, less than 50 parts per billion.

However, in the booklet inside the box, you'll find a warning recommending people with a history of respiratory disease to consult with their doctor about possible sensitivity to very low ozone.

The EPA says that the concentration of ozone would have to greatly exceed health standards to be effective in removing most indoor air contaminants."

Dr. Thomas Dailey warns, "It has never been shown by any study that these air filters are causing disease [but] I must admit, it just doesn’t make sense that if your goal is pure air that you would buy a product that would generate even a small amount of ozone."

Which is why both Dr. Dailey and the American Lung Association recommend against any ozone emitting filter.

Instead consider other purifiers like the efficiency particulate air or hepa filter. They don’t produce ozone so you won’t be emitting the most harmful component of smog into your home.

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For more information, visit:
American Lung Association: Air Cleaners Information
U.S. Environmental Protection Agency: Air Cleaners Assessment