Environmental Avoidance in the Treatment of Asthma: What Is the Evidence for Its Usefulness?

It is now generally accepted that IgE-mediated inflammation (allergy) is an important source of the chronic inflammation that is characteristic of asthma. Since indoor allergens provide an important exposure that is related to asthma morbidity in a dose-dependent fashion, a recommendation that asthmatics avoid environmental allergens is sensible. However, the clinical trials to test these recommendations have proven technically difficult, and the outcomes have been inconsistent. At this point it is not clear that allergen avoidance measures are evidence based. The experimental evidence suggests that allergen exposure can be reduced by at least 50% with currently recommended measures; but it is not clear that this level of control is adequate to reduce asthma morbidity by themselves. Another possible approach is to attempt primary prevention. By reducing allergens in homes before a susceptible child is born and maintaining these low allergen levels might prevent sensitization and thus prevent the onset of asthma. Perhaps the exposure dose to prevent asthma can actually be accomplished. Of the five trials of published to date, two have resulted in a significant reduction in asthma symptoms in infants and in school aged children.