Most people in the United States spend approximately 90 percent of their time indoors. However, the indoor air we breathe in homes and other buildings can be more polluted than outdoor air and can increase the risk of illness.

There are many sources of indoor air pollution in homes. They include biological contaminants such as bacteria, molds and pollen, burning of fuels and tobacco, building materials and furnishings, household products, central heating and cooling systems, and outdoor sources.

Indoor air pollutants in homes can include radon, secondhand smoke (also called environmental tobacco smoke), carbon monoxide, nitrogen dioxide, formaldehyde, pesticides, lead, volatile organic compounds, particulate matter, mercury, sulfur dioxide, dust, and asbestos. Buildings built before 1978 may contain caulk made with PCBs, which may be released into indoor air.

Biological contaminants in homes include bacteria, molds, mildew, viruses, animal and pet dander, dust mites, cockroaches, and pollen. Standing water, water-damaged materials, and wet surfaces can serve as breeding grounds for mold, mildew, bacteria, and insects. Biological contaminants may also be found on pets and in dirty air conditioners or humidifiers, unventilated attics, laundry areas with unvented dryers, and heating and air conditioning systems.

Combustion sources include stoves, furnaces, and space heaters that use oil, natural gas, kerosene, coal, or wood. Other combustion sources are leaking chimneys and furnaces, gas water heaters and clothes dryers, fireplaces, auto exhaust from garages, and tobacco. Indoor air contaminants from combustion sources are primarily released from malfunctioning or improperly vented heating devices.  They can also be due to inappropriate or inefficient use of these devices.

Building materials and furnishings that may cause indoor air pollution include insulation, wet or damp carpet, shingles, floor tiles, lead-based paint, mercury-containing latex paint, fireproofing, particleboard, hardwood plywood paneling, fiberboard, and furniture made of certain pressed wood products.

Household products that may cause indoor air pollution include solvents, varnishes, waxes, paints, draperies, glues, adhesives, cleaning and maintenance products, wood preservatives, air fresheners, moth repellants, dry-cleaned clothing, personal care items, hobby supplies, and stored fuels and automotive products.

Outdoor air pollution can enter buildings and become a source of indoor air pollution.  Sources of outdoor air pollutants include radon and pesticides.

Indoor air quality is also a concern in office buildings, where it is affected by maintenance and operation of building ventilation systems, moisture, and humidity. In addition to many of the indoor air pollution sources found in homes, office air pollution sources can also include office equipment, stored supplies, construction activities, mechanical systems, cleaning products, caulks, sealants, vinyl flooring, stored trash, and vehicle exhaust.

“Sick building syndrome” is a term used to describe situations in which building occupants have health symptoms that are associated only with spending time in that building. Causes of sick building syndrome are believed to include inadequate ventilation, indoor air pollution, and biological contaminants.

“Building-related illnesses” are diseases or illnesses that can be traced to specific airborne pollutants within a building. They include Legionnaires’ disease, a form of pneumonia associated with indoor air pollution, asthma, hypersensitivity pneumonitis (inflammation of the lungs), and humidifier fever, a flu-like illness related to exposure to bacteria and fungi found in humidifiers, air conditioners, and aquariums.

Long-term health effects of indoor air pollution include respiratory disease, heart disease, and cancer. Several indoor air pollutants are known or reasonably anticipated to be carcinogens because they cause cancer: radon, secondhand smoke, formaldehyde, some pesticides, lead, some volatile organic compounds, asbestos, PCBs, and some solvents.

Short-term health effects of indoor air pollution include allergic, infectious, and toxic reactions such as watery eyes, runny nose, congestion, itching, coughing, wheezing, difficult breathing, headache, dizziness, nausea, vomiting, rashes, fever, chills, and fatigue. Health problems associated with dampness, biological contaminants, and mold include asthma, allergies and hypersensitivity pneumonitis.

This description is based on the information found in the Web links listed with this topic.