At one end of the spectrum are the transient or non-specific symptoms and complaints such as common colds that may simply be brought from home or passed around the building from person to person. IAQ problems, real or imagined, seem to always affect morale, efficiency, and attendance. A difficulty in solving IAQ problems is that symptoms and complaints are typically non-specific and episodic. Often, only a select number of people are affected by a problem and their complaints may come and go. Many persons report their symptoms subside after they vacate a building and reappear upon entry.
Medical diagnosis can also be inconclusive.
This list of complaints is typically associated with the phenomenon known as sick building syndrome. A difficulty in resolving sick building syndrome is that these same symptoms can also originate from any number of possible sources including common colds, allergies, smoking, poor lighting, poor ergonomics, or stressful work loads. On the other hand there are some very specific illnesses directly associated with indoor air contamination. Each of the diseases listed below with the exception of asthma is typically associated with building related illnesses. Over the course of a day, the background levels of carbon dioxide may rise, often reaching concentrations exceeding 1,000 ppm.