According to the World Health Organization, health problems caused by mold and other airborne contaminants are a major cause of reduced productivity and absenteeism from school and work. Healthy indoor environments could save billions in health care, lost work days, productivity, and possible litigation.

Since the energy crisis of the 1970s, buildings have been sealed to save energy, keeping more pollutants inside. Air handling systems that once ran 24 hours a day, 7 days a week, are shut down to save energy. Moisture, condensing around the coil and collecting in the drain pan, fails to evaporate. Mold and bacteria breed rapidly in this dark and damp environment.

When the system is turned back on, large quantities of mold and its byproducts, along with bacteria, viruses, and yeast travel through the building and into the lungs and bloodstreams of the occupants. These biological contaminants are major contributors to "sick building" syndrome and building-related illness.

The telltale sign is a stale, musty odor, sometimes called dirty sock syndrome. Occupants complain of scratchy eyes and throat, congestion, difficulty breathing, and other complications. Most urban dwellers are indoors 90 percent of each day. No wonder over 50 million U.S. residents suffer from upper respiratory problems.