According to the US Environmental Protection Agency (EPA), most indoor air pollution comes from sources that are inside of the building. These chemicals, called volatile organic compounds (VOCs), can cause acute reactions at low to moderate levels of exposure and serious health issues in people who are exposed to high levels. VOCs are most commonly released from things like adhesives, carpeting, upholstery, man-made wood products, copy machines, cleaning products, and pesticides. This problem is compounded by the fact that most newer buildings are constructed to be as airtight as possible to conserve energy used on heating and cooling the building. Thus, pollutants are trapped inside and have little opportunity to dissipate outside.