The majority of our time is spent indoors. In order to maintain good health, we need to understand and improve the quality of the air we breathe. Scientific evidence suggests that indoor air can be significantly more polluted than outdoor air in even the largest industrialized cities. According to the Environmental Protection Agency (EPA), indoor air pollution is typically two to ten times greater than outdoor air pollution. As much as 50% of all illnesses in the United States can be attributed to indoor air pollution, according to the EPA.