Hazards and Causes of Indoor Air Pollution

Dense smog hovers over a city. Plumes of smoke pour out of factory chimneys. Sometimes it’s easy to see the sources of outdoor air pollution. But the air quality inside buildings can also be contaminated. Indoor air pollution is often not obvious, but its effects are. On average, people spend about 90 percent of their time inside, contributing to illnesses, such as asthma, and concentrated exposure to radon gas and mold.

Radon is a naturally occurring radioactive element, and is typically an invisible gas. When uranium in the ground decays, radon is produced. The gas seeps into buildings through openings, holes and cracks. Occasionally, well water contains radon. Over time, exposure to radon leads to lung cancer -- at least 21,000 deaths annually. To prevent exposure, the Environmental Protection Agency suggests that home buyers or sellers hire professionals to conduct radon tests.

Indoor air quality suffers because of many biological pollutants. People and animals bring bacteria and viruses inside. Molds and mildew are harbored in central air systems. Pollen from outdoor plants enters buildings. Cockroaches, dust mites, animal urine and dander, and cat saliva particles contaminate the air. Though viruses and bacteria can potentially infect anyone, many of the biological pollutants affect allergy or asthma sufferers by triggering asthma attacks and respiratory distress.

Any type of combustion within a building can cause indoor air pollution, much of it invisible and odor-free. This includes the use of heating and cooking fuels -- oil, gas, kerosene, wood, coal -- and tobacco products. Carbon monoxide is the most dangerous combustion-related pollutant because it limits the blood’s ability to carry oxygen. Mild to moderate exposure can produce headaches, tiredness, dizziness, nausea and disorientation. Large amounts can kill. Nitrogen dioxide is another contaminant; it irritates the eyes, nose and throat. Chemicals in second-hand tobacco smoke are extremely dangerous and can cause lung cancer and heart disease. This smoke also leads to respiratory infections, including pneumonia, and asthma, especially in children and infants. For people who already have asthma, smoke can trigger or worsen an attack.

Some pollutants are located within building materials or furnishings. Asbestos is used in roofing and flooring supplies, as well as for ceiling, wall, pipe and heating appliance insulation. When fibers from asbestos are released into the air, they can cause cancer and scarring of the lungs. Another serious danger is the chemical formaldehyde, which is sometimes used as a bonding agent in particle board, plywood, upholstery and carpet. When formaldehyde is off-gassed, it produces many symptoms, including eye, nose and throat irritation, coughing, dizziness, headaches and even rashes.

Some common household and personal goods release volatile organic compounds into the air. VOCs are found in thousands of ordinary products, including paint and paint stripper, cleaning supplies, aerosol sprays, glues, markers, stored fuel and pesticides. Benzene is one of the most toxic VOCs; it causes cancer in humans. It comes from tobacco smoke, vehicle emissions, paint supplies and fuels. Another VOC, perchloroethylene, is a suspected carcinogen. It's commonly used in dry cleaning.