This article (2009) discusses how over past half-century there have been major changes in building materials and consumer products used indoors. Modern materials as composite-wood, synthetic fabrics, polymers, foams, plastics and scented products, mechanical and electrical appliances emit an array of chemicals. The changes in emission profiles for indoor pollutants caused by these materials are combined with the effects of modification in how modern buildings work. They rely heavily on ventilation and recirculation. Together these changes have altered the composition of the chemicals building occupants are exposed to every day. Many chemicals present today were not present 50 years ago, and similarly, some that had high levels then have decreased since (such as formaldehyde, chlorinated pesticides, PCBs). Some have increased and remain high (phtalate esters, brominated flame-retardants).

“Many of the chemicals presently found in indoor environments, as well as in the blood and urine of occupants, were not present 50 years ago.”

Indoor pollutants that were known to be harmful and could be measured – formaldehyde, radon, asbestos, tobacco smoke and nonpolar volatile organic compounds, pesticides and other semivolatile organic compounds – were monitored indoors. Even though the methods to measure indoor pollutants have improved over time, there remain compounds whose levels have not been directly measured, and whose presence indoors is only inferred (e.g., hydroxyl, nitrate, hydroperoxyl and methyl peroxyl radicals).