The reduction in asthma symptoms and bronchial hyperresponsiveness in adolescence is not well understood. Nor can the differences in asthma prevalence and severity between the sexes, which reverse at puberty, be explained. It has been suggested that the improvement in asthma during adolescence may result from diminished clinical and immunological responsiveness directly related to hormonal changes and that the effect of age on the prevalence of asthma in each sex may relate to differences in hormonal status, potentially influencing airway size, inflammation, and smooth muscle and vascular functions. However, few comprehensive studies are available. In summary, all wheezing is not asthma. Non-asthmatic wheezing illnesses may in part be attributable to anatomical abnormalities of the lung (transient early wheezing, premature birth). Little is known about the genetic and environmental determinants of childhood asthma, and factors related to the development of atopic sensitisation, such as exposure to allergens, infectious diseases, or tobacco smoke early in life, and dietary habits may be important, whereas the relevance of air pollution remains to be established. Unfortunately, we still do not know how to prevent the manifestation of childhood asthma.