How environmental exposures influence the development and exacerbation of asthma.

Environmental exposures may increase a child's risk of developing asthma and also may increase the risk of asthma exacerbations. This article reviews several environmental exposures and suggests whether they contribute to asthma prevalence, asthma exacerbations, or both. Outdoor air exposures and violence are not likely to cause the increase in asthma prevalence. Exposure to outdoor air pollutants primarily leads to increased exacerbations, sometimes manifested as asthma clusters. Clinicians should be alert for space-time clusters of asthma exacerbations in the community, because these clusters may suggest a modifiable point-source exposure. Indoor air exposures are more strongly linked to the increase in asthma prevalence. Exposure to dust mites and tobacco smoke are risk factors for the development of asthma and may also exacerbate existing asthma. Effective measures to prevent exposures to these pollutants are available. With proper management, the amount of environmental exposures can be decreased. Whether decreasing these exposures will result in decreases in asthma prevalence and exacerbations is not yet documented.