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The 4th Georg Rajka International Symposium on Atopic Dermatitis presented a comprehensive view of our current understanding and management of atopic dermatitis (AD). These proceedings highlight contributions related to the history of AD doctrines; genetic and epigenetic background; epidemiology; maturation of the immune system; infection and innate-adaptive immunity; epidermal inflammation, including neurogenic inflammation and pruritus; animal models; skin barrier; evidence-based therapy and education programs; prognostic and severity markers; and allergy testing. Several studies in animal models and human subjects point to impaired skin barrier function as a primary defect that facilitates the effect of environmental factors and immune dysregulation found in AD. The new frontier in AD therapy should, in the near future, reflect our better understanding of the skin barrier. The influence of environmental factors on the skin and other epithelial barriers in the perinatal period needs to be better understood to implement appropriate prevention programs. [Copyright &y& Elsevier]

The skin acts as an interface between the body and its surrounding environment. The epidermis, the surface layer of the skin, is chiefly responsible for this interactive protective function. The epidermal barrier may be subdivided into three defensive systems: the photoprotective barrier, the immune barrier, and the physical and chemical barrier of the stratum corneum or horny layer. To protect against harmful ultraviolet radiation, the epidermis has absorption factors such as melanin, produced by melanocytes, and urocanic acid, which is a degradation product of filaggrin. The epidermal immune defence system comprises an innate component, which is rapid but non-specific, together with adaptive response, which is systemic and antigen-specific, initiated by Langerhans cells. The stratum corneum, derived from terminal differentiation of epidermal keratinocytes, plays a key role as a physical and chemical permeability barrier. This horny layer is made up of corneocytes, covered with horny envelopes and linked to one another by corneodesmosomes and by extracellular matrix sheets. The epidermal barrier, which is constantly being renewed, is characterised by its extremely great capacity of adaptation to changing conditions in the environment., (Copyright © 2017. Published by Elsevier Masson SAS.)