Is asthma caused by atopy (positive skin prick tests)? Epidemiologic evidence suggests a negative answer.

In this paper we shortly discuss epidemiological data on the relationship between asthma and atopy according to recent personal and literature epidemiological publications. The coexistence in several subjects of asthma (and of other "atopic" diseases) and IgE hyperproduction generated the dogma that these two biological conditions are mainly genetic in origin and are linked by a strong casual relationship. In the last decades atopy increased at 5-10 % annual rate and at present atopy prevalence, although variable in different countries, reaches somewhere the prevalence of more than 60 %. Similarly, asthma prevalence increased in the last decades, especially so in western and English speaking countries, reaching in certain countries prevalence values higher than 40 %. For these reasons, although certainly dependent on a genetic predisposition, atopy and asthma can nowadays be considered to be largely determined by environmental factors. Moreover, the analysis of epidemiological data derived from studies conducted worldwide, showed that the prevalence of the two conditions were clearly not correlated so that in certain countries with a 50-60% prevalence of atopy asthma prevalence is lower than 2-6 %, while in other countries asthma prevalence is double than atopy prevalence. Further, in countries with high atopy, the prevalence this conditions is high both in asthmatics and in normal subjects and in the places where asthma prevalence reaches high levels this condition is high both in atopic and non atopic people. In conclusion, epidemiological data show that environmental factors affecting asthma prevalence are different from those affecting atopy prevalence and that subjects bearing one of the two conditions don't show any preferential tendency to develop the other one. From aetiological and pathogenetic point of view asthma and atopy appear to be independent conditions We therefore believe that the association between asthma and atopy demonstrated in almost all the "population studies" (atopy prevalence has always been found 20-30 % higher in asthmatics than in non asthmatic subjects) doesn't prove the existence of a "causal" relationship between the two conditions: this could be a kind of association without causative meaning as is the association between blond hair and blue eyes which in no way can be considered a prove that one of the two conditions is the cause of the other.