The skin microbiota is an inseparable component of the skin barrier structure, which participates in the stabilization or impairment of the barrier function as well as the development of many skin diseases. To characterize the normal skin microbiota and its association with skin sites, age and sex, we recruited 50 volunteers divided into children, adolescents, young adults, middle-aged adults and the elderly. The skin sites consisted of cheeks, volar forearms (representing dry environments) and upper back (representing sebaceous environments). A total of 9 574 365 high-quality sequences of the V3 to V4 region of the 16S rRNA gene were annotated with taxonomic information related to two archaeal phyla (Thaumarchaeota and Euryarchaeota) and five dominant bacterial phyla (Actinobacteria, Proteobacteria, Firmicutes, Bacteroidetes and Cyanobacteria). The skin bacteria community structure was influenced by skin sites, and was closely related to age and sex. The upper back was dominated by Propionibacterium and Staphylococcus, and the cheeks facilitated the survival of Betaproteobacteria, while Alphaproteobacteria were prevalent on the volar forearms. Regarding the effects of age, after sexual maturity, the cheek microbiota became more similar to sebaceous sites (i.e. the upper back). The volar forearms appeared to experience the aging process earlier than the other two sites. The elderly had greater species richness and diversity and their community composition no longer had skin-site selectivity. Males had a greater species richness than females, but the sex differences in the community structure only present at certain age groups and skin sites.

Our study suggests premature corneodesmolysis as the main pathological mechanism of this palmoplantar skin disorder. We conclude that KE appears to be a distinct peeling entity.

Introduction: Necrobiosis lipoidica (NL) is a chronic, granulomatous disease linked to diabetes mellitus (DM). Our aim was to characterize its histology and inflammatory cell features to better understand its etiology. Methods: A retrospective study was performed within Mayo Clinic from 1992 to 2017. Inclusion into the study required biopsy-proven NL where the histopathology and inflammatory infiltrate of 93 biopsies were reviewed by a dermatopathologist. Results: The granulomatous changes of NL were most commonly diffuse (84% No DM, 97% DM-2, 60% DM-1, p¼0.048). The pattern of inflammation was most often palisaded 54% and or tiered/layered 65% (59% No DM, 80% DM-2, 40% DM-1) involving the mid-dermis (98% No DM, 100% DM-2, 80% DM-1) (p¼0.016). Sarcoidal granulomas were more common in those without DM (24% No DM, 3% DM-2, 0% DM-1) (p¼0.025). The subcutis was involved in the non-DM and DM-2 30% of the time. Mucin was present more commonly in diabetics (17% non-DM, 53% DM-2, and 40% DM-1) (p¼0.01). Perivascular inflammation was present in 82% of cases and composed predominantly of lymphocytes (93% No DM, 100% DM-2, 80% DM-1) (DM-2 vs DM-1 p¼0.013) and plasma cells 73%. Lymphocytic infiltrates were ubiquitous and plasma cells (81% No DM, 83% DM-2, 40% DM-1) (DM-2 vs DM-1 p¼0.033) were significantly different in the infiltrate. Eosinophils were present (38% No DM, 10% DM-2, 20% DM-1) (p¼0.02) and were seen in differing amounts in the dermis (p¼0.049). Neutrophils were present (14% No DM, 50% DM-2, 60% DM-1) (p<0.001) and were seen in differing amounts in the dermis (12% No DM, 47% DM-2, 60% DM-1) (p <0.001). Giant cells were seen in 82% of cases. Foamy histiocytes were seen in 71% of cases and were often widespread (63% No DM, 30% DM-2, 33% DM-1) (p¼0.042). Conclusion: While sharing similar histopathology, the inflammatory profiles between the NL subgroups of Non-DM, DM-2 and DM-1 are distinct. NL may have different mechanisms between groups.