ABSTRACT
There is extensive evidence that the prevalence of bronchial asthma is increasing in many of the countries of the world. Marked increases have been observed over the last two to three decades among children and adolescents in industrialized countries (l-3), but a markedly greater prevalence of asthma has also been found among children raised in urbanized communities than among their genetic counterparts living in the traditional native setting (4,5). Potential causes for this widespread increase in the prevalence of asthma have been suggested (5). Many of these proposed causes could have their effect by increasing the tendency toward allergic sensitization; these include decreased early exposure to viruses (6), decreased breast feeding and early introduction of cow's milk and solid food (7), increased exposure to pollution from burning of fossil fuels (8), and-perhaps most importantly-alterations in conditions in the home. The last few decades have witnessed not only increased insulation and decreased exchange with the outdoor air (9) but also increased indoor temperature and use of carpeting (10). These changes would result in increased indoor humidity, increased growth of house dusts mites and molds, and trapping of allergens and irritants in the home.
