What Are Possible Sources of Indoor Air Pollution?

Course: WB 2579
CE Original Date: June 5, 2015
CE Renewal Date: June 5, 2017
CE Expiration Date: June 5, 2019
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Learning Objective

Upon completion of this section, you will be able to

  • Identify possible sources of indoor air pollution.

Indoor air pollution can pose a serious health threat. EPA studies indicate that the levels of many air pollutants may be two to five times higher in indoor air than outdoor air. In some cases, indoor air pollutants may even be 100 times higher than outdoors. High levels of indoor pollutants are of particular concern because people may spend as much as 90% of their time indoors [American Lung Association 2010; U.S. Consumer Product Safety Commission (CPSC) 2012; US Environmental Protection Agency 2012a].

The clinician should consider the following possible sources of indoor air pollution when eliciting information on exposures. Possible indoor contaminants include

  • Asbestos,
  • Biologic agents,
  • Building materials,
  • Radon,
  • Tobacco smoke, and
  • Wood stoves, gas range, or other heating devices.

The content in this section focuses on the above potential sources of indoor air pollution. The next section discusses additional potential exposure sources and pathways to hazardous substances in the home and environment that may also contribute to poor indoor air quality and pose exposure and health risks.

Environmental Tobacco Smoke

Environmental tobacco smoke (ETS) is the mixture of smoke that comes from the burning end of a

  • Cigarette,
  • Pipe, or
  • Cigar.

as well as smoke exhaled by the smoker. It is a complex mixture of over 4,000 compounds, more than 40 of which are known to cause cancer in humans or animals and many of which are strong irritants. ETS is often referred to as secondhand smoke and exposure to ETS is often called passive smoking. In general, children’s lungs are more susceptible to harmful effects from ETS than adults. In infants and young children up to 3 years, exposure to ETS causes an approximate doubling in the incidence of

  • Pneumonia,
  • Bronchitis, and
  • Bronchiolitis [U.S. Consumer Product Safety Commission (CPSC) 2012; US Environmental Protection Agency 2012a].

ETS is an entirely preventable public health hazard and strongly linked to major respiratory diseases such as asthma and lung cancer [Dhala et al. 2006; DHHS 2014].

Gas Space Heaters, Wood Stoves, and Gas Ranges

In addition to environmental tobacco smoke, other sources of combustion products include

  • Fireplaces,
  • Gas stoves,
  • Unvented kerosene and gas space heaters, and
  • Woodstoves.

The major pollutants released include

  • Carbon monoxide,
  • Nitrogen dioxide,
  • Radon, and
  • Particulates.

Unvented kerosene heaters may also generate acid aerosols.

Combustion gases and particulates also come from chimneys and flues that are improperly installed or maintained and cracked furnace heat exchangers. Pollutants from fireplaces and woodstoves with no dedicated outdoor air supply can be back-drafted from the chimney into the living space, particularly in weatherized homes [US Environmental Protection Agency 2012a].

Wood stoves, when not properly maintained and vented, emit noxious substances including

  • Carbon monoxide,
  • Oxides of nitrogen,
  • Particulates, and
  • Hydrocarbons.

Studies have shown that children living in homes heated with wood stoves have a significant increase in respiratory symptoms compared with children living in homes without wood stoves [Belanger and Triche 2008].

Gas ranges, which may produce nitrogen oxide, a respiratory irritant, are used for cooking in more than half of the homes in the United States [Belanger and Triche 2008].

Building Materials

Building materials, home improvement products, and textiles used in the home can pose health risks. For example, formaldehyde volatilizes from pressed wood products made using adhesives that contain urea-formaldehyde (UF) resins. Pressed wood products made for indoor use include

  • Particleboard (used as subflooring and shelving and in cabinetry and furniture),
  • Hardwood plywood paneling (used for decorative wall covering and used in cabinets and furniture), and
  • Medium density fiberboard (used for drawer fronts, cabinets, and furniture tops).

Formaldehyde exposure can cause

  • Watery eyes,
  • Burning sensations in the eyes and throat,
  • Nausea, and
  • Difficulty in breathing in some humans exposed to elevated levels (above 0.1 parts per million).

Higher environmental concentrations may trigger breathing problems in exposed asthmatics. There is evidence that some people can develop sensitivity to formaldehyde. It has also been shown to cause cancer in animals and possibly in humans [US Environmental Protection Agency 2012a].


Asbestos is most commonly found in older homes [US Environmental Protection Agency 2012a]) in

  • Pipe and furnace insulation materials,
  • Asbestos shingles,
  • Millboard,
  • Textured paints and other coating materials,
  • Floor tiles, and
  • Ceiling titles and panels.

Intact, undisturbed asbestos-containing materials generally do not pose a health risk. Elevated concentrations of airborne asbestos can occur after asbestos-containing materials are disturbed by

  • Cutting,
  • Sanding or
  • Other remodeling activities.

Improper attempts to remove these materials can release asbestos fibers into the air in homes, increasing asbestos levels and endangering people living in those homes. Exposure to these fibers has been associated with

  • Lung cancer,
  • Asbestosis, and
  • Mesothelioma [US Environmental Protection Agency 2012a].

Smoking cigarettes with exposure to asbestos has a multiplicative effect on the risk of developing lung cancer (higher than the lung cancer risk from smoking alone or from asbestos exposure alone) [Agency for Toxic Substances and Disease Registry 2001].

For more information on Asbestos, please see “What Are Additional Environmental Health Resources?” section.


The most common source of indoor radon is uranium in the soil or rock on which homes are built. As uranium naturally breaks down, it releases radon gas (which is a colorless, odorless, radioactive gas). Radon gas enters homes through

  • Dirt floors,
  • Cracks in concrete walls and floors,
  • Floor drains, and
  • Sumps.

Exposure to radon becomes a concern when radon becomes trapped in buildings and concentrations increase indoors. Lung cancer is the predominant health effect associated with exposure to elevated levels of radon. Radon causes thousands of preventable lung cancer deaths each year. EPA estimates that radon causes about 14,000 deaths per year in the United States; however, this number could range from 7,000 to 30,000 deaths per year. For persons that smoke and have high home radon levels, the risk of developing lung cancer is especially high [US Environmental Protection Agency 2012a].

For more information on radon, please see “What Are Additional Environmental Health Resources?” section.

Biological Agents

Biological agents include

  • Animal dander, saliva, urine,
  • Bacteria,
  • Cockroaches,
  • House dust mites,
  • Mildew,
  • Molds,
  • Pollen, and
  • Viruses.

Sources of indoor biologic pollutants include plants, people, and animals. Building materials and/or conditions that support the growth, concentration or dissemination of indoor biologic pollutants should also be considered. It is important not to overlooks these potential sources of biologic pollutants. Contaminated central air handling systems can become breeding grounds for

  • Mold,
  • Mildew, and
  • Other sources of biological contaminants

that can be distributed throughout the home.

Some biological contaminants trigger allergic reactions, including

  • Allergic rhinitis,
  • Hypersensitivity pneumonitis, and
  • Some types of asthma.

Infectious illnesses, such as influenza, measles, and chicken pox are transmitted through the air. Molds and mildews release disease-causing toxins. Symptoms of health problems caused by biological pollutants include [US Environmental Protection Agency 2012a]

  • Coughing,
  • Digestive problems,
  • Dizziness,
  • Fever,
  • Lethargy,
  • Shortness of breath,
  • Sneezing, and
  • Watery eyes.
Key Points

It is important not to overlook potential exposure sources of indoor air pollution.

Page last reviewed: June 23, 2015