Environmental pollution increases allergic diseases: fantasy or reality?

In the last decade, the involvement of environmental pollution in the increasing prevalence of allergies, has aroused interest not only in public but also in the operators of the sector that gave origin to several epidemiological and experimental researches, aimed at understanding the action of pollutants and their relationship with allergic diseases. The results of these studies have highlighted that chemicals can act at different levels (directly on humans, on sources and carriers of allergens and on allergen characteristics) and that the final effect is a «puzzle» made by the integration of all the single effects. Of course the puzzle is not yet complete and the acquisition of additional information is needed to define the total contribution of pollution to the increase of allergy prevalence. Nevertheless, today we can try to assess the individual contributions, analyzing the data already obtained on the effect at the single levels. Concerning the direct action on humans, the acquired data clearly show that air pollution contributes to the raising of sensitization in subjects predisposed to respiratory diseases and to the worsening of symptoms in individuals already allergic. The mechanism involves both the triggering of proinflammatory processes that increase the permeability of the epithelium by facilitating the penetration of allergens and their interaction with the immune system mediators and an immunologic adjuvant effect on the synthesis of IgE in atopic subjects. As regards the action of pollution on allergen sources and allergens, the effects are numerous and include (i) the pollen cell wall damage with a consequent release of small cytoplasmic particles containing allergens, (ii) the increased synthesis or post-translational modification of known allergens or the induction of allergenic proteins expression not normally produced and even (iii) the increase of pollen season length and pollen production. Nevertheless, although these effects are all indicative of a pollutant contribution to the allergy rise, few cause-effect studies linking the effect detected in the environmental component (such as pollen) with the symptoms felt by allergic patients, are available to date. Overall however, the scientific information currently available is sufficient to state that pollution contributes to the increase of allergy through a series of actions, carried out at different levels, some of which widely demonstrated and others just supported by indications that must be better defined.