Oral microbiota in allergic diseases, and sublingual allergen immunotherapy

Allergic diseases with their epidemic prevalence on the rise have been one of the major global health problems of the 21st century. The association of increased prevalence with lifestyle changes including increased urbanization, and hygiene practices highlighted the importance of host-microbiome interactions for maintaining immune homeostasis. In support, numerous studies demonstrated altered gut microbiome composition in allergic patients, and suggested dysbiosis as a possible cause of allergic diseases. Nevertheless, despite being the second largest microbiota in the human body, oral microbiota has not yet received the attention it deserves in the literature. With this review article, we aim to highlight its significance by summarizing the data obtained from studies evaluating oral microbiome composition in patients with allergic respiratory diseases. Additionally, their importance will be further elaborated by discussing the findings presented by animal and human studies investigating the possible effect of oral probiotic uptake to the clinical efficacy of sublingual allergen immunotherapy.