A number of studies have shown gender differences in the prevalence of wheeze and asthma. The aim of this review was to examine published results on gender differences in childhood and adolescent asthma incidence and prevalence, define current concepts and to identify new research needs. A Medline search was performed with the search words (gender OR sex) AND (child OR childhood OR adolescence) AND (asthma). Articles that reported on absence or presence of gender differences in asthma were included and reviewed, and cross-references were checked. Boys are consistently reported to have more prevalent wheeze and asthma than girls. In adolescence, the pattern changes and onset of wheeze is more prevalent in females than males. Asthma, after childhood, is more severe in females than in males, and is underdiagnosed and undertreated in female adolescents. Possible explanations for this switch around puberty in the gender susceptibility to develop asthma include hormonal changes and gender-specific differences in environmental exposures. This aspect needs consideration of the doctors and allergists who diagnose and treat asthmatic individuals. In conclusion, sex hormones are likely to play an important role in the development and outcome of the allergic immune response and asthma in particular. By obtaining functional data from appropriate models, the exact underlying mechanisms can be unravelled. To examine the effect of gender-specific differences in environmental exposures and changes of asthma prevalence and severity in puberty, larger populations may need to be investigated.

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The European Community Respiratory Heath Survey (ECRHS) was the first study to assess the geographical variation in asthma and allergy in adults using the same instruments and definitions. The database of the ECRHS includes information fromy140,000 individuals from 22 countries. The aim of this review is to summarize the results of the ECRHS to date.The ECRHS has shown that there are large geographical differences in the prevalence of asthma, atopy and bronchial responsiveness, with high prevalence rates in English speaking countries and low prevalence rates in the Mediterranean region and Eastern Europe. Analyses of risk factors have highlighted the importance of occupational exposure for asthma in adulthood. The association between sensitization to individual allergens and bronchial responsiveness was strongest for indoor allergens (mite and cat). Analysis of treatment practices has confirmed that the treatment of asthma varies widely between countries and that asthma is often undertreated.In conclusion, the European Community Respiratory Health Survey has shown that the prevalence of asthma varies widely. The fact that the geographical pattern is consistent with the distribution of atopy and bronchial responsiveness supports the conclusion that the geographical variations in the prevalence of asthma are true and most likely due to environmental factors. Eur Respir J 2001; 18: 598-611. During the first half of the 1990s, information on the variation in asthma prevalence, known or suspected risk factors for atopy and asthma, and information on the management of asthma in young adults was collected in the European Community Respiratory Health Survey (ECRHS).The reason for undertaking the ECRHS was a rapid increase in the prevalence of asthma that had been reported from many different countries [1][2][3][4]. This increase was over too short a time period to be explained by genetic factors and must therefore have been related to nongenetic or environmental changes. Further evidence of the importance of environmental factors in asthma was that studies comparing prevalence in urban and rural areas in developing countries had shown large differences in asthma prevalence [5][6][7]. Treatment patterns of asthma [8] and asthma mortality [9] had been found to vary considerably in Europe which raised the question of whether the variation in mortality was due to geographical differences in the prevalence of asthma or differences in asthma fatality. Research directed towards identifying the environmental factors that explain this geographical variation in asthma was required to identify potential strategies to counter the global increase in the prevalence of asthma.The information available on the variation in the prevalence of asthma and allergy at the beginning of the 1990s had been collected through several studies using different protocols. The ECRHS was, therefore, the first study that assessed the prevalence of asthma and allergic disease in a large number of countries