[Epidemiology of allergic respiratory diseases: many questions, few answers].

Over the last twenty years an increase of allergic respiratory diseases has been observed, even if a broad variability of incidence has been reported. Asthma and allergic rhinitis are more common among young subjects, but there are data of an increase of allergic respiratory diseases in older patients. Moreover it has to be underlined the increase of the severity of these diseases, as shown by the higher use of anti-allergic drugs and by the increase of fatal asthma. The reasons of this trend are not understood. One reason can be the more appropriate diagnosis of asthma by the general practitioners. Other factors must be considered: the most important one can be air pollution; many air components (i.e. SO2, NO2, O3), particularly in industrialized countries, may play a role in allergic sensitization through an irritative-inflammatory mechanism. Socio-economic factors can also influence the incidence of allergic diseases. Other factors as cigarette smoke, foods, allergenic load have to be mentioned. Finally a viral etiology has been reported. Very recently, the allergic inflammation has been considered as the crucial event in the pathogenesis of allergic respiratory diseases. As allergic diseases can lead to chronic inflammation, an early and long-lasting treatment is mandatory.