How to Improve Your Indoor Air Quality

What they do: Air filters remove irritants like mold spores, pet dander, candle and cigarette soot, and even skin cells from the air, making it easier to breathe, especially for people who have allergies.

How to use them effectively: High-efficiency particulate air (HEPA) filters generally cost more than ionic filters, but HEPA filters are more efficient at removing all of the airborne particles, says Dr. Portnoy. The best way to filter air for the whole house is with a filter that's placed in the furnace, he says. (In desert regions, the filter may be attached to the air conditioner as part of an electric heat pump.) Be sure to leave the system's fan running even if the heat is not on to allow the filter to do its job.

Safety alert: "Some air filters produce ozone," Dr. Portnoy says. "The ozone oxidizes the chemicals that produce smells and makes the air smell fresh, but doesn't remove them." Because ozone itself can be an irritant, he recommends steering clear of ozone-producing devices (most are labeled on the package).

Upkeep tips: Over time, HEPA filters clog up and need replacing. How often you need to change them will depend on how contaminated the air is. Electrostatic filters should be cleaned according to the manufacturer's directions (some have parts that can be hosed off or wiped down, while others use disposable filters).

Additional advice: Don't bet on your air filter to protect you from mold allergens. "Where there's water, there's going to be mold," Dr. Portnoy says. The best remedy is to get rid of the source of the mold (such as a leak or damaged drywall) and use a diluted bleach solution to remove the mold spores.