Book Review

Clearing the Air: Asthma and indoor air exposures

N Engl J Med 2000; 343:1819-1820December 14, 2000

Article

Clearing the Air: Asthma and indoor air exposures
Committee on the Assessment of Asthma and Indoor Air for the Institute of Medicine. 438 pp. Washington, D.C., National Academy Press, 2000. $57.95. ISBN: 0-309-06496-1

The rising trends in asthma and associated allergic diseases create a problem that affects many developed and developing countries and that so far has defied explanation other than apportioning blame to changing lifestyles and the environment. But what aspects of the environment could be responsible for these changes? A number of hypotheses have been advanced — the “hygiene hypothesis” finding popular favor — but deprivation of the mucosal immune response from microbial programming early in life fits best with changing trends in atopy, rather than with trends in asthma. It is convenient and politically expedient to link asthma with air pollution in order to blame something environmental for the increased prevalence of asthma. Clearing the Air: Asthma and Indoor Air Exposures provides a comprehensive, systematic review of the evidence that indoor air pollution has a role in respiratory illnesses. As demanded by this method of “systematically” assessing published data, the evidence extracted from the literature is graded according to its quality and impact. This enables the Institute of Medicine to draw conclusions about the strength of the evidence linking indoor air pollution to effects on respiratory health.

The book is a fairly dry read: the text and conclusions are those of an expert committee and are not an enlightened debate linking epidemiology to mechanisms. Strong emphasis is placed on the causative effects of indoor pollution in susceptible hosts, but there is no explanation of why atopy or exposure to allergens accounts for only 40 percent of the attributable risk of asthma in children and adults. The introduction also refers to genetic susceptibility, but the discussion is entirely focused on immunologic responses and does not consider susceptibility to air pollutants and the parts of the lung that they may affect. There is hardly any mention of the airway epithelium, which after all is the interface where the effects of exposure to air pollutants influence physiologic or pathologic responses.

These comments should not detract from the high quality of this review, especially its coverage of air-quality monitoring as related to the indoor environment. However, some conclusions are drawn on the basis of current knowledge, which in itself is deficient. Maybe this is an example of conclusions that are drawn before we really understand how, and on what targets, indoor air pollutants act and how we may identify the people who are most susceptible. I was also a little surprised that more emphasis was not placed on methods to assess personal exposure, since total exposure to pollution is a composite of indoor and outdoor exposures.

As a stimulus to promote further research, this book is first class. However, as an informative and stimulating read, it is lacking, especially when one considers how biotechnology will affect this field in the near future.

Stephen T. Holgate, M.D.
University of Southampton, Southampton SO16 6YD, United Kingdom