Intended for healthcare professionals


Air pollution in homes

BMJ 1996; 312 doi: (Published 25 May 1996) Cite this as: BMJ 1996;312:1316
  1. David Coggon
  1. Reader in occupational and environmental medicine MRC Environmental Epidemiology Unit, University of Southampton, Southampton General Hospital, Southampton SO16 6YD

    May be more important than outdoor pollution but is more difficult to monitor

    The dangers of air pollution are a regular topic of discussion in the lay press, much of it ill informed. For example, the increasing prevalence of asthma in Britain and elsewhere is widely attributed to the rise in pollutants from motor vehicles, although the balance of scientific evidence suggests that any influence of traffic pollutants on the initiation of asthma is small.1 Traffic pollutants, especially fine particulates, do seem to cause illness, but their impact on public health is probably less than that of smoking, diet, and poor housing.

    To date, attention has focused mainly on pollutants in outdoor air, for which it is easy to blame others rather than ourselves. Indoor hazards that have attracted publicity have also tended to be those caused by someone else—such as asbestos in schools and council flats or environmental tobacco smoke in offices. It is often overlooked that pollutants such as benzene and nitrogen dioxide are commonly found at higher concentrations indoors than outside. Moreover, in countries like Britain most people spend most of their time inside buildings. Thus, even where outdoor levels of a pollutant are higher, indoor levels may still be the main determinant of exposure.

    Recognising the need for better information about indoor air quality, the Department of the Environment commissioned a survey by the Building Research Establishment, which published its results this week.2 The study measured formaldehyde, volatile organic compounds, nitrogen dioxide, and biological particulates over a 12 month period in 174 homes in southwest England. Findings included a higher count of house dust mites in living room than bedroom carpets, with indications that the carpets themselves were a habitat for the mites as well as mattresses and other soft furnishings. The survey also confirmed that levels of nitrogen dioxide are determined in part by outdoor concentrations, but are highest in kitchens with gas cookers. The mean nitrogen dioxide concentrations in two homes were above the World Health Organisation's guideline value of 150 µg/m3 over 24 hours in at least one 14 day period.

    Also published this week is a report from the Medical Research Council's Institute for Environment and Health, which reviewed the health effects of indoor air pollutants at the levels found in the Building Research Establishment's survey.3 The conclusions are generally reassuring, but there is some concern about children's risks of respiratory illness from nitrogen dioxide from gas cookers and about the effects of high counts of house dust mites on people with asthma. Together with the survey, this report will help to shape the government's programme to promote good air quality in homes.

    Improving air quality in private dwellings is a challenge. In the control of outdoor pollution the government's approach has been to set standards based on the advice of an expert panel of scientists. These standards are intended to prevent ill health even in vulnerable groups such as asthmatic patients, and the extent to which they are met is assessed by routine measurements at a network of monitoring stations. Monitoring pollutants in homes is more difficult, and their control must depend in part on individual choices. It may be practical to enforce standards for ventilation in new houses and for emissions from new gas appliances, but it would be unreasonable to limit the availability of furnishings and household equipment that pose a risk to only a small minority of the population. Instead, people should be able to make informed choices depending on their personal circumstances. One step in this direction is a guide to controlling mites in the home, which the Department of the Environment circulated earlier this year to general practitioners and allergy clinics and which is targeted at adults with asthma and parents of asthmatic children.

    In the future we should see similar guides about other indoor air pollutants. In addition, there is an urgent need for further information about indoor pollutants not covered by the survey. In particular, interpreting epidemiological data about non-biological particulates in outdoor air would be much enhanced if we knew more about their concentrations within buildings and how these relate to levels outside.


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