Allergens like pet dander, pollen and mold spores are included in the category of indoor air pollutants called "particles," defined as any substance measuring less than 100 microns in diameter. (One micron equals 1/25,000 of an inch in diameter.) The U.S. Environmental Protection Agency has found that small particles (less than 2.5 microns) are responsible for the health effects of greatest concern. That’s because these invisible contaminants can be inhaled deep into the lungs and move through the bloodstream.

If you or any of your family members have allergies, you could also do well by minimizing contact with chemicals, which are found in common household items like artificial air fresheners and bleach cleaners. Depending on the level present in your home, chemical fumes can prompt an allergic reaction, plus cause headaches, fatigue, dizziness, nausea and respiratory problems.