Most indoor environments have more than one source that contributes to indoor air pollution.
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems. Health effects may show up either years after exposure has occurred or only after long or repeated periods of exposure. These effects, which include some respiratory diseases, heart disease, and cancer, can be severely debilitating or fatal. Recent data suggest that poor IAQ can reduce a person's ability to perform specific mental tasks requiring concentration, calculation, or memory. It is prudent to try to improve the indoor air quality even if symptoms are not noticeable.