Asthma is a global health problem with genetic and environmental components. indoor allergens have a major impact on asthma, and exposure in sensitized subjects can compromise lung function. A reduction in allergen exposure would seem a logical facet to treatment. Methods for reducing mite allergen levels that are effective in the laboratory may not work in the home and may not result in a clinical benefit. Six ongoing studies are investigating the effects of environmental control on the primary prevention of asthma and allergies. Although the Isle of Wight and Canadian studies provide encouraging results at age 8 and 7 years, respectively, it will be some time before a definitive public health message emerges. For secondary prevention, there is little evidence to support the use of mite-proof encasings as a single intervention in adults. In children' however, single or multifaceted interventions appear to be of some benefit. Copyright © 2006 by Current Science Inc.