Dirty indoor air is a winter hazard.

The air in your home may be dirtier than the air outdoors, especially in winter, when residences are closed tightly. Secondhand tobacco smoke, chemical fumes, airborne dust, animal dander, and many other pollutants are fouling indoor air and causing misery for millions of people.

The issue goes beyond mere discomfort; air quality can affect your health significantly. A 1989 report by the Environmental Protection Agency noted the level of indoor air pollutants may be two to five times greater than outdoor levels, and the EPA's Science Advisory Board has put indoor air pollution on its list of top five environmental risks to...