ABSTRACT
Asthma is difficult to define in childhood, owing to the existence of several different clinical phenotypes, as well as the shifting prevalence of these phenotypes from infancy to the school-age years and beyond. In addition to having unique clinical features, it is likely that each of these forms of childhood asthma has some distinct pathophysiological features. As a result, the types of stimuli and environmental exposures that initiate acute symptoms of wheezing and bronchospasm also vary with the age of the patient and the specific phenotype of asthma.
