There are a variety of causes of poor indoor air quality. A NISOH study based on over five hundred complaints found that inadequate ventilation and the release of contaminants from indoor and outdoor sources are the primary reasons for indoor air quality problems (see pie chart). Inadequate ventilation may be defined as insufficient air to remove pollutants that are degrading the quality of air. Thus, the air quality in a building is the result of a contest between the pollutants and the ventilation system. Other factors that can aggravate this situation are temperature, humidity, and microbial contamination.
The early shutdown and late startup of a ventilation system and insufficient fresh outdoor air entering a ventilation system are often the direct result of overzealous energy-saving procedures. The problems of poor air distribution by a ventilation system within a building, limited air mixing in occupied areas, and clogged filters can contribute to poor air quality.
Since the early 1970s buildings have been built to be more airtight to conserve energy. This has resulted from using improved construction techniques and caulking and sealing. Unfortunately, this practice limits the amount of polluted air that escapes, which can cause pollutants to build up to unhealthy levels inside a building.
Temperature and humidity extremes can affect the emission rates of some pollutants as well as the perceptions of building occupants. High humidity and high temperature cause people to feel lethargic and want more air movement. Low humidity induces coughing, dry throats, and dry eyes. An additional problem with low humidity is that it accentuates sense of smell. Noise from mechanical systems or glare from lights can cause headaches and fatigue. These are all symptoms of sick building syndrome and are thus usually blamed on poor air quality.