Searching for the cause of the increase in asthma.

The prevalence of asthma has increased dramatically over the last 30 years, and the clearest evidence for the increase has come from population-based studies of school-aged children and young adults. The strongest established risk factors for asthma are family history and sensitization to one or more indoor allergens. Some studies suggest that the increase in asthma has been part of an overall increase in atopic disease. The American data, however, suggest that hay fever was already common in 1960. Thus the primary increase has been in wheezing among allergic children. It seems unlikely that increases in mite, cockroach, and domestic animal allergens have been sufficient to explain the scale or the consistency of the increase in asthma prevalence. The challenge is to identify a change that could have increased inflammation of the lungs or lowered the threshold for wheezing.