The increase in the prevalence of asthma and allergies observed during the last decades has been largely investigated, but the reasons for such trend are still unclear. The distribution of factors traditionally considered responsible of the allergic disorders (such as pollen or moulds), do not explain the geographical differences observed internationally in the prevalence of asthma and allergies. The conduction of new studies aimed at monitoring the trend in asthma and allergies, and in the risk factors associated with these disorders, such as the SIDRIA study (Italian Studies on Respiratory Disorders in Children and the Environment), will shed new light on this phenomenon.