Air Pollution
Clean Air for Kids

Indoor Air Quality
What is Indoor Air Pollution?

Most people associate air pollution with the air outdoors. However, we spend a large part of our lives indoors at home or in buildings such as schools and offices. Keeping the air which we breathe indoors clean is therefore important, particularly for certain vulnerable persons, including babies, children, pregnant women and unborn babies, the elderly, and those suffering from breathing difficulties or allergies, such as asthma.

In most homes the level of indoor air pollution is very low, because there are controls on the design and construction of buildings. However, if ventilation of rooms is poor, or household appliances are faulty, pollution can build up to levels which may be detrimental (harmful) to human health.

There are many possible sources of air pollutants in the home and indoor air quality can vary widely. These are detailed below.

Sources of Indoor Air Pollution

In the majority of homes there is no need for concern over existing levels of pollutants because housing and public health legislation exists to help prevent air quality problems arising indoors in the first place. The main sources of indoor air pollution are outlined below.

Household Appliances

Appliances that burn fuel are potential sources of indoor air pollution. This includes, for example, gas cookers, wood stoves, solid fuel open fires and gas or paraffin heaters . Nitrogen dioxide is produced from the use of gas cookers. If an appliance is faulty, incomplete combustion may result in the release of carbon monoxide, a highly poisonous gas. Ventilation is the key to reducing levels of indoor air pollutants from appliances. Extractor fans can help reduce air pollution from cooking appliances. Solid fuel fires need a chimney or flue to allow harmful gases to exit the building. However, gas heaters fuelled by propane gas are not connected to a chimney or flue. Care should be taken when using these, to ensure that enough fresh air is circulated in the room.

Poor Ventilation

It is important that air is circulated in the indoor environment to make sure that harmful levels of gases or particles do not build up. There should be chimneys or flues to allow harmful gases from heating appliances to escape into the outside air, as already mentioned. Other sources of air pollutants are listed below.

Whilst it is sensible to draft proof rooms to save energy, it is also important not to seal a room up so much that air does not circulate freely. It is therefore a good idea to leave doors ajar or windows open for short periods to enable air to circulate.

Toxic Chemicals and Fibres

DIY and building work may lead to a temporary increase in indoor pollutants such as volatile organic compounds (VOCs), during painting or paint stripping in enclosed spaces, or laying of loft insulation. Toxic chemical sources include solvents which occur in paints, varnishes and glues, and formaldehydes and preservatives which are used in wood products. Newly built homes can have high levels of indoor air pollution from these sources. Good ventilation is necessary for several weeks until levels of these pollutants have reduced.

Loft insulating fibres such as glass fibres may also be harmful to human health. Asbestos used to be commonly used for insulation, but is now known to cause lung tissue scarring and possibly cancer.

Other sources of toxic chemicals include household cleaning products, fly sprays, air fresheners and deodorants which can also be harmful to health. As a general rule, spray products are more toxic than solid or liquid products.


Cigarette smoke can cause a build up of air pollution when people smoke indoors. The pollutants include carbon monoxide, nicotine, tar, formaldehyde, ammonia and nitrogen oxides. There are serious health effects relating to the breathing of air polluted by cigarette smoke, including eye and throat irritations, respiratory problems such as bronchitis and pneumonia, asthma, low birth weight in babies, heart attacks and lung cancer.

Dust mite

House dust mites are microscopic spider-like creatures which live in beds, carpets and other soft furnishings. They are a common source of indoor air pollution.

The faeces, skin casts and pieces of dead mites contain substances which can trigger asthma attacks, inflammation of the lining of the nose and eczema in sensitive people. House dust mites are present in almost every home, although because they are so small you will be unlikely to see them. They tend to thrive in warm, humid conditions.

A dust mite problem can be alleviated by keeping the house and beds well aired, and ensuring that carpets are kept clean and dry. Regular dusting and vacuuming of soft furnishings will also reduce the incidence of dust mite.

Mould Spores

Moulds are a type of fungus. Moulds spread by releasing millions of tiny spores into the air. They need moisture to grow and are usually found in damp, poorly ventilated areas of homes, such as bathrooms. You cannot see the spores but you may be able to see moulds, grey, green or black in colour, growing on damp surfaces.

Mould spores are a source of indoor air pollution. Airborne mould spores can produce allergic reactions in sensitive people similar to hay fever. People who experience allergic reaction to mould spores are also more likely to suffer from asthma.

Mould spores can be reduced by improving ventilation in the home, and by limiting sources of moisture and condensation.


Radon is a naturally occurring radioactive gas that is produced by the radioactive decay of uranium present in all earth materials such as rocks, soils, brick and concrete. High concentrations of radon are often found in areas with granite, limestone or sandstone bedrock and are particularly high in parts of the UK such as Cornwall and the Peak District. Outdoor air has radon in it (but not much). Indoors, however, radon concentrations can build up to much higher than outdoor levels, if ventilation is poor.

Breathing high concentrations of radon can cause lung cancer. More importantly, radon decays radioactively into other elements that are also radioactive, and unlike radon these other elements (such as polonium) stick in the lungs if inhaled. Additionally, there is evidence that radon is much more dangerous to smokers than to non-smokers.


The main sources of nitrogen dioxide and carbon monoxide in the indoor environment are gas cookers and poorly maintained heating appliances respectively. Formaldehyde sources include insulation materials, particleboard and chipboard, water-based paints, cigarette smoke and vehicle exhaust. Sources of volatile organic compounds include building materials, cleaning products, solvents, glues, furniture and tobacco smoke. These pollutants have wide ranging effects on human health depending on factors such as the concentration of the pollutant, amount of ventilation, or size of enclosed space.

Dust mites and mould spores can also reduce the quality of indoor air and are associated with health problems such as asthma.

Health Effects of Indoor Air Pollution


Asthma is a common disease in the UK, affecting more than 3 million people. It can occur in people of any age, but is most likely to develop in children by the age of 5 and in adults during their 30s. People over 65 are also prone to the disease. Asthma is an allergic condition that is often inherited by children from their parents. This type of asthma is often related to eczema and hay fever, with 50% of adults and 80% of children who have other allergies commonly developing asthma. Symptoms of asthma in a person can increase or decrease in severity through life. Approximately 1 in 3 children who suffer from asthma will have no symptoms by the time they reach adulthood.

Asthma affects the airways and disrupts the transport of air in and out of the lungs. Asthma sufferers have sensitive airways which become inflamed and narrowed under certain conditions. The inflammation is caused by the body's immune system, in order to counteract the irritant. When inflammation occurs it becomes difficult for oxygen to reach the lungs. Consequently asthmatics may experience difficulty with breathing.

Numerous factors can be responsible for triggering an asthma attack. Asthmatics are usually allergic to more than one trigger and their asthma symptoms may vary from wheeziness, to shortness of breath, chest tightening or the over production of mucus.

Both indoor and outdoor air pollution, natural and man-made, can trigger asthma attacks. Common indoor pollutant triggers include the dustmite, mould and cigarette smoke. As much as 85% of children that experience asthmatic symptoms are allergic to dust mite. Cigarette smoke is damaging to everyone's airways but can be particularly bad for people with asthma. Smoke causes the airways to narrow, making it more difficult to breathe.

Outdoors, natural plant, grass and tree pollen can act as triggers in some asthmatics. Man-made pollution may also be harmful to asthmatics. Although it has not been proven that a link exists between air pollution and asthma, certain pollutants, including sulphur dioxide, nitrogen dioxide and ozone are known to restrict the airways and make it more difficult for asthma sufferers to breathe. Fine particulate matter is also suspected to be a lung irritant.

Although there is no cure for asthma at present, inhalers can be used to reduce the severity of the symptoms. Preventer inhalers may be used to build up a long-term resistance to asthma triggers, whilst reliever inhalers are used as an instantaneous means of relieving asthmatic symptoms, by relaxing the muscles controlling the airways.

Other Health Effects

Pollutants have differing effects on human health depending on the type and concentration of the pollutant. Carbon monoxide which may result from poorly maintained heating appliances or from running a car engine in an enclosed garage, can cause a range of health effects from headaches and dizziness to death if concentrations are allowed to build up to very high levels.

The use of chemicals can cause health problems ranging from eye and nose irritation to more serious effects such as lung disease.

Smoking, and passive smoking (breathing in other people's smoke), is known to have effects on human health. These range from eye, nose and throat irritations to lung cancer.

Controlling Indoor Air Pollution

Indoor air pollution in the workplace which is hazardous or toxic is controlled by legislation called The Control of Substances Hazardous to Health (1988). In the indoor home environment, the home owner is responsible for controlling air pollution. Some pollutants such as radon are naturally occurring and in areas where levels of radon are high, advice may be given by local environmental health departments on how to reduce levels in homes. Grants may be available to increase ventilation in homes and to ensure that ground level floors are thoroughly sealed.

Some pollutants are found in higher concentrations indoors, particularly gases and particles from cigarette smoking. Ventilation is the best way to prevent the build up of high concentrations of such pollutants. Allowing fresh air to circulate means that pollutants can be dispersed and thus do not build up to high concentrations.

Good maintenance of heating appliances and their chimney flues is also important. When toxic chemicals are used indoors, the appropriate protective equipment should be used (for example breathing mask with filter, safety glasses) and rooms should be well ventilated to allow any fumes to disperse.

Smoking indoors can cause the build up of many toxic pollutants. It is better not to smoke in an indoor environment. If persons do choose to smoke indoors, they should ensure that the room is adequately ventilated with fresh air to reduce the effects on their own and other peoples' health.

Dust mite and mould spores can be reduced by good hygiene including regular vacuuming of carpets and mattresses and changes of bedding at frequent intervals. Dusting with a damp cloth can also prevent particles being released into the indoor environment.

Houseplants are thought to have beneficial effects for indoor air. Research by NASA shows that living plants and flowers can absorb harmful and toxic gases. Plants that have been identified as good at absorbing the pollutants benzene, carbon monoxide and formaldehyde include bamboo palm (Chamaedorea seifritzii), Ivy (Hedera helix), pot chrysanthemums (Chrysantheium morifolium) and dracaenas (e.g. Dracaena 'Janet Craig').