5 Causes of Poor Indoor Air Quality by Royal Air Duct Cleaning. Often, we assume that being indoors means we are protected from harsh elements or other irritants that may interfere with our comfort, or worse, our health. Poor indoor air quality can be caused by a variety of factors that, decease if unchecked, can lead to headaches, sinus problems, infections, lung disease, and lung cancer. In fact, shockingly, the U.S. Environmental Protection Agency has stated that the air inside buildings might be five times more polluted than the air outdoors. Below are a few poor indoor air quality culprits: Biological Pollutants It isn’t uncommon for bacteria, view mold, and other types of fungi to settle indoors. If your house contains areas that are prone to moisture or the accumulation of water and condensation, these may serve as prime locations for unhealthy cultures to grow. Once molds have become present, allergenic spores can be released into the air, which can t...