We usually think of air pollution as being outdoors, but the air in your house or office could also be polluted. Sources of indoor pollution include Biological contaminants like mold and pollen Tobacco smoke Household products and pesticides Gases such as radon and carbon monoxide Materials used in the building such as asbestos , formaldehyde and lead Sick building syndrome occurs when several people are affected, but no specific source of the illness is found. Indoor air quality problems usually only cause discomfort, and most people feel better as soon as they eliminate the source of the pollution. However, some pollutants can cause diseases that show up much later, such as respiratory diseases or cancer. Making sure that your building is well-ventilated and eliminating pollutants can improve the quality of your indoor air.