If your home was built after 1980, you probably have dirty air. At the height of America's fuel crisis in the '70s, home builders jumped on the energy-efficiency bandwagon and began making houses airtight. Your grandmother's house was built like a sieve, leaking precious heat through every crack. In the process, though, it underwent three to four complete changes of air per hour. A modern, energy-efficient home exchanges only half its air each hour.

"We're living in a baggie," says Dianne Walsh Astry, spokeswoman for Health House, a national project of the American Lung Association of Minnesota. "We've sealed off all those holes and sealed off all the ventilation. All the pollution stays in the house."

Does that make us less healthy than our grandparents were? Astry believes so. The era of the airtight home coincides with a sharp rise in asthma and allergies in this country. According to the Centers for Disease Control and Prevention, the number of people with asthma more than doubled between 1980 and 1998.

Fortunately, there's a lot you can do to clear your home's air. First, understand the major sources of pollution and irritants. Then take some simple, common-sense steps to remove them.

Pollutants in the Home

We think of air pollution as an outdoor or workplace hazard, but there are pollutants and irritants in houses and apartments as well. Some come from living creatures; others are chemical fumes and vapors. Most are easy to identify and reduce but some are deadly.

Biological irritants include molds, dust mites, cockroaches, and pets. Molds and dust mites thrive on humidity and can cause allergic reactions or asthmatic episodes. Cockroaches are not only disgusting to look at — their droppings are a major allergen. And your pet dog or cat is a source of dander, another known allergen. Allergy sufferers who can't part with their pets can get some relief by limiting animals access to carpeted areas and bedrooms. Carpets, in general, collect allergens, so you might think about getting rid of them.

There are a host of nonbiological sources of indoor air pollution as well. Cleaning products give off noxious fumes. New carpeting and furniture made of particleboard give off formaldehyde vapor for several weeks after they're manufactured, which can cause eye, nose, and throat irritation.

Probably the most significant indoor pollutant is cigarette smoke. The dangers of secondhand smoke are too well known to need repeating here. If you can't get a friend or relative to kick the habit, you're entirely justified in showing them the back porch when they feel the need to light up.