Human microbiome and allergic diseases in children: pathogenetic role and therapeutic options

The recent and extensive study of the microbiome has provided an enormous amount of data concerning the type and possible functions of microorganisms present in the gut, airways, genital tract, and skin. These data showed interpersonal differences in the composition of the microbiome and these differences suggest a link between the microbiome, the immune modulation, and the pathogenesis of allergic diseases. This research is particularly relevant in paediatrics, since allergic diseases are constantly increasing and there is evidence in the paediatric age that shows that the composition of the microbiome in the foetal and neonatal period plays a key role in the development of the immune system: vaginal delivery, breastfeeding, childhood spent in rural environments and/or in contact with animals result in a greater biodiversity of the microbiome with the presence of protective species that reduce the activation of Th2 lymphocytes, involved in allergic reactions. Further studies are necessary to better understand the microbiota role in the pathogenesis of atopy in order to understand if specific probiotics and prebiotics, administered orally or topically, can affect the microbiota composition and modulate immune system functions, producing a therapeutic effect in the treatment of allergic diseases. This narrative review analysed the available literature regarding the correlation between the microbiome and the development of allergic diseases and with special focus on paediatric studies. The skin, gut or lung dysbiosis can be a cofactor in the pathogenesis of allergies and the remodulation of the microbiome becomes an important therapeutic challenge.