Although smog and ozone levels have declined dramatically since the early 1990s, Americans are still breathing remarkably polluted air. Incredibly, this air is not in congested cities, but inside homes and office buildings. The Environmental Protection Agency (EPA) reported in December 1998 that airborne pollutants were two to five times higher indoors than out. According to the EPA, the air inside is less healthy than the air outside because emissions from automobiles and industrial smokestacks have declined and because buildings are now built so tightly and so well-insulated that indoor air-borne pollutants are unable to escape.

The indoor pollutants recorded by the EPA are found in most American homes. They include polycyclic aromatic hydrocarbons from kerosene heaters and fireplaces, and nitrogen oxides from gas stoves. Also listed are secondhand smoke from cigarettes and cigars; mold and mildew spores; dust mites; chemical fumes...