One of the most common and harmful pollutants is benzene, for which there is no safe threshold of exposure. It depresses the nervous system and causes cardiac ''sensitization'' as well as headaches, dizziness and nausea; it is surmised that it can also cause leukemia. Car exhaust, smoke from tobacco, fuel burning appliances and perhaps more surprisingly, incense, are common culprits. Cleaning products also tend to contain it because benzene was once the solvent of choice in manufacturing, although thanks to legislation limiting its use it's less common today. You may, however, still be able to find it in everyday furnishing materials such as vinyl, PVC and rubber floorings, as well as nylon carpets and SBR-latex-backed carpets. Particleboard furniture, plywood, fiberglass, flooring adhesives, paints, wood panelling, caulking and paint remover also may contain benzene. You should also be careful of mosquito repellants and other solvents, including where you store them! If you're working in an environment where a lot of photocopying or printing is done, then know that you're likely to be exposed too.

While the authors conclude that there isn't sufficient evidence to prove that carbon monoxide directly causes death, it is commonly accepted that it can lead to heart failure. As carbon monoxide replaces oxygen in your system, at the very least it is proven to have an effect on one's exercise abilities! The causes for carbon monoxide inhalation are similar to benzene, namely combustion sources (heating and cooking appliances, car exhaust making its way indoors, etc.). In 'developed countries' exposure is most commonly caused by faulty, incorrectly installed, poorly maintained and/or ventilated appliances, but clogged chimneys, wood-burning and decorative fireplaces which don't have safety features, and gas burners/additional heaters that are devoid of safety valves/detectors can also pose a threat. It's therefore a good idea to install carbon monoxide detectors near all combustion devices. In 'developing countries' the burning of biomass and tobacco smoke are more likely culprits. Nitrogen dioxide, meanwhile, is emitted by similar appliances and products but it mostly tends to affect asthmatics and others with respiratory problems, especially children. It can also have an impact on the immune system.

Naphthalene, for its part, affects the respiratory tract - it's been proven to cause tumors in animals and hemolytic anaemia in humans. Some studies indicate lymphoma can be caused by repeated exposure, while other less reliable evidence suggests it's linked to laryngeal and colon cancer. In your home, you're most likely to be exposed through the use of mothballs! It's also used as a disinfectant, including as a block deodorizer for toilets, and is present in some paints. If you have a garden know that it's contained in the insecticide carbaryl. Wood smoke, fuel oil and gasoline also contain naphthalene, as does tobacco smoke. The major constituent of creosote, used for timber impregnation, is naphthalene.

Polycyclic aromatic hydrocarbons (PAHs) are proven to directly cause lung cancer. Benzo[a]pyrene (B[a]P) is considered to be the best indicator for the presence of all sorts of PAHs and any level of exposure, however small, is considered harmful to humans. Causes are again related to things like smoking, incense and candle burning as well as combustion appliances, such as stoves. Radon is another carcinogen that mainly affects the lungs, although it's also been associated to leukemia and cancers of the extra-thoracic airways. Radiation seeps into the home from decaying rocks, and building regulations are meant to stipulate that a radon barrier be part of the building's fabric to help protect you from it. It's advisable to get your home tested regularly; check with your national radiological institute on how to go about this.

Finally, trichloroethylene (TCE) and tetrachloroethylene (PCE) tend to attack the kidneys; in the case of trichloroethylene it also causes liver and bile duct cancer, as well as non-Hodgkin’s lymphoma. It may also lead to ''impaired neurobehavioral performance''. TCE is mainly used in manufacturing to clean metal parts, while PCE is mostly used as a dry cleaning agent and as an industrial solvent. Both can can be used in the production of textiles, and TCE can be used to make paint while PCE can be used to remove it. Some specialized adhesives and cleaning fluids may also contain PCE, including spot removers, water repellants and wood cleaners.

So what can you do limit the amount of pollutants in your home and workplace? It's best to first of all avoid pollution at the source, i.e. place fresh air inlets (ventilation) away from pollution sources or preferably choose to work and live as far away as possible from polluted environments, e.g. busy roads. You should also try to eliminate the emissions caused by your own doing, i.e. from smoke (faulty appliances, candle or incense burning, smoking, etc.) and from buying and using harmful products (some DIY products including board materials, paints and solvents, as well as mothballs, vinyl furnishing materials, and so on). The WHO's guidelines are not exhaustive - they admit that some pollutants, such as asbestos and flame retardants, still require further research to determine if they should be included in their IAQ guidelines. As always, buyer beware!