Energy efficiency at home and at work comes with a price-stale air. One of the key ways to keep heating and air conditioning costs down is to trap air indoors. However, by sealing windows shut and preventing ventilation, air in buildings can become as polluted as the pea soup skies of the largest cities. Breathing bad indoor air can lead to immediate health problems like irritated eyes and asthma, or long-term diseases as serious as heart disease and cancer.

Pollutants hide in all corners of a home, school, or workplace and come in all forms, including: puppy dander, damp carpeting, mold, furniture made of pressed wood, household cleaning products, beauty products, tobacco smoke, and pesticides.

To combat these culprits and protect one's health, air cleaners are an increasingly popular choice, but do they really work?

The Pros

The right air purifier can trap certain airborne pollutants, and some filter out allergens in the air like dust and pollen.

Air cleaners come in different sizes and abilities. Several different technologies have been shown to work, including mechanical filters, electronic air cleaners, and ionizers. Those that contain electrostatic filters, negative ion generators, pleated filters, or a combination thereof are best at cleaning up tobacco smoke, according to the Environmental Protection Agency (EPA). Air cleaners with sorbents can also remove some gaseous pollutants. Ionizers rid the air of floating particles by changing their electrical charge, which makes them stick to walls and other surfaces.

The Cons

Not all air-purifying machines are up to the job. In fact, one "cleaning" technology can make conditions worse.

Some manufacturers sell machines they claim purify air by making ozone gas. In a poorly ventilated room, these air purifiers can produce ozone that builds to unsafe levels, according to a recent study by scientists at the University of California, Irvine. In fact, air pumped from a purifier that uses a process called ozonolysis can be worse than Los Angeles smog.

In fact, contrary to manufacturers' assertions, ozone generators aren't effective at rendering hazardous chemical contaminants harmless. The machines don't remove odors, carbon monoxide, or formaldehyde from a room. Ozone doesn't react at all with such chemicals, according to the EPA. Ozone does not remove particles of dust or pollen (however, ozone generators are sometimes packaged with an ionizer, which does remove these allergens, although not very efficiently).

Even if you read the directions for these purifiers carefully and follow all the detailed instructions, you're still in danger of turning your home into an ozone hotbed. No federal agency has approved these devices, because even at low concentrations, ozone can cause harmful health problems such as chest pain and breathing problems. What's worse, people susceptible to the negative health effects of these air purifiers are out there buying them for what they think will be relief.

The Verdict

The key to finding an air purifier that doesn't pollute is in the fine print. Read the label to avoid purchasing a machine that uses ozonolysis. Look on the back of the box for an Association of Home Appliance Manufacturers (AHAM) seal of approval. Check out the three "clean air delivery rate" or CADR numbers: one for tobacco smoke, one for pollen, and one for dust. The CADR represents the amount of filtered air produced by the machine. The higher the numbers, the faster the unit filters the air. A machine sporting a CADR of 80 for dust means that the air purifier will lower the amount of dust in the air to the same level that pumping 80 cubic feet of clean air each minute would accomplish.

At home, you can limit your exposure to air pollution by remembering to change air cleaner filters frequently. While you're at it, change your vacuum bag to prevent overfilling and adding more dust to the air. Tidy the rest of your home too. Wipe surfaces clean of dust, mold, and bacteria. Keep clutter under control so dust has fewer places to settle. Don't use fireplaces or wood burning stoves frequently and cut out smoking indoors. Open up your windows, feel the breeze on your face, and take in a deep, clean breath of fresh air.

Further Reading on the Web:

EPA

Association of Home Appliance Manufacturers

Clean Air Delivery Rate

The American Lung Association