Probiotics and allergies: myth or reality?

During the last years, along with the growing knowledge about the role and importance of the intestinal flora, interest remarkably increased in probiotic bacteria supplementation. It has indeed been demonstrated that the intestinal microbiota is very important in the regulation of several functions of the organism, even those far from the gastro-enteric system. Among them, great interest was stimulated by the proven capability of the intestinal microbiota to regulate the immune system, in particular to rebalance the TH1/Th2 ratio. Consequence thereof is the assumption that the administration of probiotic bacteria may induce clinical benefits in allergic pathologies. Many clinical studies have been carried out that considered the possibility of preventing allergic sensitizations, and preventing and treating atopic dermatitis and allergic rhinitis. Many studies demonstrated that the administration of probiotics is able to prevent the onset of allergic sensitizations and improve the symptoms of atopic dermatitis and allergic rhinitis; however, studies were published, too, that achieved negative outcomes. The overall evaluation of results is, however, difficult, as the strains used and the study design are markedly heterogeneous. Future investigations with a better standardization will be able to better explain the role of the intestinal flora in atopy, and the role of probiotics in the treatment of allergic diseases.