The CDC's Environmental Health division warns that poor indoor air quality comes from many sources. (This is one reason to consider getting an upgraded air filter, offered for certain Alen Air Purifiers––you get a customized solution by selecting an air filter that meets the specific needs of your household. See our Product Advisor, based on your air quality desires.)
The Center for Disease Control notes that poor indoor air quality can cause frequent headaches, dry eyes, nasal mucus, nausea and extreme tiredness. And even more serious––the CDC states that poor indoor air quality "can lead to suffering from lung diseases."
At the CDC, they are especially concerned about the dangers of molds, pollen, pet dander, secondhand smoke, formaldehyde and fumes emitted by imported drywall; carbon monoxide that comes from burning propane, other gases and fuels, as well as charcoal; and the use of household products such as cleaning and pesticides.
The CDC is emphatic about the dangers related to indoor air pollution, and they want the public to be aware of this catastrophic health hazard. They go on to caution: "If you think poor indoor air is making you sick, please see or call a doctor."