Air contaminants present inside homes and buildings. Many think that air pollution is only a problem outdoors, however, indoor air pollution is actually responsible for many human health problems. 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. But in some cases, indoor air pollution can cause diseases that show up later, such as respiratory diseases or cancer. Asbestos, cigarette smoke, radon and carbon monoxide are some examples of indoor air pollution.