Lack of adequate ventilation Since the 1970s energy crisis, buildings have been designed to use less energy for heating, e.g. sealed buildings, re-circulating building air and allowing less fresh air to enter the building. The result of these changes is that indoor air pollutants are less diluted by bringing in fresh new outdoor air. High humidity can produce warm and wet conditions which help grow moulds and mildew. Major types of pollutants Biological contaminants can come from both outside and inside the home. Sources include house dust mites, animal dander, dust, pollen, cockroaches and moulds, all of which can cause an allergic reaction.
Some organisms can contaminate water sources, and become airborne through humidifiers.
Sources include wood heaters, furnaces, woodstoves and fireplaces. Formaldehyde and other VOCs are also given off by burning wood, kerosene and tobacco products. Personal care products, cleaning agents, paints, lacquers and varnishes are other sources of VOCs. VOCs can be released from these materials for several years. It is sometimes found wrapped around older hot water pipes and boilers.