ABSTRACT
During the last ten years, significant progress has been made in our understanding of the factors that are associated with the development of childhood asthma. In spite of these advances, essential aspects of the etiology of asthma remain unresolved. For example, there is ample evidence that the prevalence of asthma is increasing and that only a small proportion of these changes in prevalence can be explained by reporting biases.1 Although many hypotheses have been proposed to explain these increases, what is causing this ‘asthma epidemic’ is largely unknown.
