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Microbiome research is a highly transdisciplinary field with a wide range of applications and methods for studying it, involving different computational approaches and models. The fact that different people host radically different microbiota highlights forensic perspectives in understanding what leads to this variation and what regulates it, in order to effectively use microbes as forensic evidence. This narrative review provides an overview of some of the main scientific works so far produced, focusing on the potentiality of using skin microbiome profiling for human identification in forensics. This review was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The examined literature clearly ascertains that skin microbial communities, although personalized, vary systematically across body sites and time, with intrapersonal differences over time smaller than interpersonal ones, showing such a high degree of spatial and temporal variability that the degree and nature of this variability can constitute in itself an important parameter useful in distinguishing individuals from one another. Even making the effort to organically synthesize all results achieved until now, it is quite evident that these results are still the pieces of a puzzle, which is not yet complete.

Atopic dermatitis (AD) is a recurrent, chronic, inflammatory, itchy skin disorder that affects up to 20% of the pediatric population and 10% of the adult population worldwide. Onset typically occurs early in life, and although cardinal disease features are similar across all ages, different age groups and ethnicities present distinct clinical characteristics. The disease imposes a significant burden in all health-related quality of life domains, both in children and adults, and a substantial economic cost both at individual and national levels. The pathophysiology of AD includes a complex and multifaceted interplay between the impaired dysfunctional epidermal barrier, genetic predisposition, and environmental contributors, such as chemical and/or biological pollutants and allergens, in the context of dysregulated TH2 and TH17 skewed immune response. Regarding the genetic component, the loss of function mutations encoding structural proteins such as filaggrin, a fundamental epidermal protein, and the more recently identified variations in the epidermal differentiation complex are well-established determinants resulting in an impaired skin barrier in AD. More recently, epigenetic factors have facilitated AD development, including the dysbiotic skin microbiome and the effect of the external exposome, combined with dietary disorders. Notably, the interleukin (IL)-31 network, comprising several cell types, including macrophages, basophils, and the generated cytokines involved in the pathogenesis of itch in AD, has recently been explored. Unraveling the specific AD endotypes, highlighting the implicated molecular pathogenetic mechanisms of clinically relevant AD phenotypes, has emerged as a crucial step toward targeted therapies for personalized treatment in AD patients. This review aims to present state-of-the-art knowledge regarding the multifactorial and interactive pathophysiological mechanisms in AD.

Background Psoriasis is a chronic inflammatory skin disorder with unclear etiology. The roles of skin microbiome and metabolic dysregulation in psoriasis pathogenesis are not yet fully understood. Methods We conducted an integrated microbiome and untargeted metabolomic analyses on skin samples from 29 patients with psoriasis and 31 healthy controls. The skin microbiota was characterized using 16 S rRNA gene sequencing, and untargeted metabolomic profiling was performed using LC-MS/MS. Multivariate statistical analyses were used to identify differential microbes and metabolites, followed by correlation analyses to explore microbe-metabolite interactions. Results Psoriatic lesions exhibited significantly higher skin microbial alpha diversity compared to healthy controls. Principal component analysis revealed distinct microbial community structures between the two groups. At the genus level, Corynebacterium and Staphylococcus were significantly enriched in psoriatic lesions, while Cutibacterium was notably reduced. Metabolomic analysis identified 63 differential metabolites, with 39 upregulated and 24 downregulated in psoriatic lesions. These metabolites were primarily involved in lipid metabolism (particularly phospholipids and sphingolipids), amino acid metabolism, and inflammatory mediator pathways. Correlation analysis revealed significant associations between microbial alterations and metabolic dysregulation. Cutibacterium abundance was negatively correlated with inflammatory lipids and positively correlated with antioxidant metabolites, whereas Staphylococcus and Corynebacterium exhibited the opposite pattern. Notably, the abundance of Propionibacteriaceae strongly correlated with glutathione levels ( r  = 0.821, P  < 0.001), indicating a potential role of microbiome-mediated oxidative stress in psoriasis. Conclusions This study highlights significant alterations in both the skin microbiome and metabolome in patients with psoriasis, revealing complex microbe-metabolite interaction networks. The findings suggest that microbial dysbiosis, particularly the decreased abundance of Cutibacterium and the increased abundance of Staphylococcus / Corynebacterium , may contribute to psoriasis pathogenesis by modulating lipid metabolism, inflammatory pathways, and oxidative stress responses.

Background The IL-17A inhibitors target aberrant immune responses in psoriasis but also impacts the host’s defense against infections. The effects of this treatment on skin microorganisms and microbiome-encoded metabolic pathways remain unclear. Objectives This was an exploratory clinical study designed to investigate whether Psoriasis is associated with skin microbiota, as well as a longitudinal cohort study aimed at revealing the effects of IL-17A inhibitor treatment on skin microbiota in Psoriasis. Methods In this study, we recruited 26 patients with moderate to severe psoriasis and 15 healthy controls. We collected skin microbiome samples from both greasy and dry skin regions. All samples were analyzed using 16S rDNA gene sequencing to determine the microbial profiles. Results Compared with healthy controls, the composition and function of skin microbiome in psoriasis patients are heterogeneous. Treatment with IL-17A inhibitors significantly increases the alpha diversity of the skin microbiota in psoriasis patients, indicating potential restoration of microbial community richness and evenness. However, this treatment does not entirely alter the taxonomic composition of the skin microbiota; rather, it shifts the relative abundance of specific microbial species, indicating that certain core microbial features remain relatively stable. Moreover, IL-17A inhibitors help adjust the functional profile of the skin microbiome in psoriasis patients, bringing it closer to that of healthy individuals. Conclusions Psoriasis patients exhibit significant heterogeneity in both the composition and functionality of their skin microbiota. Although IL-17A inhibitor treatment fails to fundamentally alter its taxonomic composition, this therapy effectively enhances microbial community stability by increasing alpha diversity and modulating the relative abundance of various taxa. Additionally, it adjusts the functional profile of the skin microbiota towards a healthier state, thereby contributing to the restoration of microecological balance.

The field of human microbiome research is rapidly expanding beyond the gut and into the facial skin care industry. However, there is still no established criterion to define the objective relationship between the microbiome and clinical trials for developing personalized skin solutions that consider individual diversity. In this study, we conducted an integrated analysis of skin measurements, clinical Baumann skin type indicator (BSTI) surveys, and the skin microbiome of 950 Korean subjects to examine the ideal skin microbiome-biophysical associations. By utilizing four skin biophysical parameters, we identified four distinct Korean Skin Cutotypes (KSCs) and categorized the subjects into three aging groups: the Young (under 34 years old), the Aging I group (35-50), and the Old group (over 51). To unravel the intricate connection between the skin's microbiome and KSC types, we conducted DivCom clustering analysis. This endeavor successfully classified 726 out of 740 female skin microbiomes into three subclusters: DC1-sub1, DC1-sub2, and DC2 with 15 core genera. To further amplify our findings, we harnessed the potent capabilities of the CatBoost boosting algorithm and achieved a reliable framework for predicting skin types based on microbial composition with an impressive average accuracy of 0.96 AUC value. Our study conclusively demonstrated that these 15 core genera could serve as objective indicators, differentiating the microbial composition among the aging groups. In conclusion, this study sheds light on the complex relationship between the skin microbiome and biophysical properties, and the findings provide a promising approach to advance the field of skincare, cosmetics, and broader microbial research.

Objective To investigate the differences in scalp and gut microbial diversity, community structure, and specific microbial species in patients with psoriasis vulgaris before and after treatment with interleukin (IL)-17A inhibitors, compared to healthy individuals. Additionally, the preliminary impact of IL-17A inhibitors on scalp and gut microecology was explored. Methods This study utilized 16S rRNA gene sequencing to comparatively analyze the dynamic changes in scalp and gut microbiota diversity and community composition in patients with moderate-to-severe psoriasis vulgaris before and after treatment with IL-17A inhibitors. The study included 15 patients with a Psoriasis Area and Severity Index score of ≥10 and a sex- and age-matched healthy control group. Scalp scale and fecal samples were collected at three-time points: pre-treatment (baseline), 4 weeks post-treatment, and 12 weeks post-treatment. Results IL-17A inhibitors demonstrated favorable efficacy in treating plaque psoriasis. Following treatment, no statistically significant difference was observed in the alpha and beta diversity of the scalp microbiome between patients with psoriasis and healthy controls. Notably, the abundance of harmful bacteria ( Pseudomonas species) decreased on the scalp, while beneficial Bifidobacterium levels increased. Regarding gut microbiota, significant differences in α-diversity richness were observed compared to healthy controls (P<0.05). Moreover, the abundance of Roseburia , Megamonas , and the phylum Bacteroidota increased, although the Firmicutes/Bacteroidota (F/B) ratio showed no significant change. Conclusion: IL-17A inhibitor therapy has the potential to improve the structure and diversity of the scalp microbiome, gradually restoring it toward a healthier state while also enhancing gut microbiota diversity. These therapeutic effects may be mediated through immune regulation, such as the Th17 pathway modulation, and microbial metabolites like short-chain fatty acids.

Multiple skin conditions have been associated with alterations in the diversity and composition of the skin microbiome, including dry skin and atopic dermatitis. In these conditions, a number of commensal skin bacteria have been implicated in supporting a healthy skin barrier, including . Recent clinical studies in patients with mild-to-moderate atopic dermatitis and dry/itchy skin have shown significantly improved skin barrier function and microbial diversity upon treatment with moisturizers containing 1% colloidal oat. We hypothesized that direct use of colloidal oat by skin microbes contributes to these therapeutic benefits. Skin bacterial growth was assessed using the BacT/ALERT system. and growth rates and metabolism were compared in an in vitro competition assay. The effect of a 1% colloidal oat-containing moisturizer on lactic acid content of the stratum corneum was clinically assessed in subjects with moderate-to-severe dry skin. gene expression was evaluated by next-generation mRNA sequencing. Short-chain fatty acids were quantified in bacterial culture supernatants. In vitro, colloidal oat increased the growth rate of vs , as well as the metabolism of . Colloidal oat also significantly increased lactic acid concentrations in supernatants of both strains and decreased pH, consistent with clinical findings that 6-week use of a 1% colloidal oat-containing lotion significantly increased lactic acid on dry skin. Further analyses suggest that colloidal oat alters the gene expression profile of . Colloidal oat directly affects the growth, metabolism, lactic acid production, and gene expression of skin commensal bacteria, as shown via in vitro studies. The increased production of lactic acid reflects clinical observations with colloidal oat-containing skin moisturizers. Our findings suggest a new mechanism for colloidal oat as a skin prebiotic, which may contribute to improvements in skin and microbiome diversity in various skin conditions, including dry/itchy skin and atopic dermatitis.

INTRODUCTION Psoriasis is characterized by raised, scaly, well-demarcated, erythematous oval plaques. Although studies have revealed that disruption of immune tolerance and excessive production of inflammatory factors play important roles in the pathogenesis of psoriasis, the exact mechanism is still not clear Previous studies have shown that the concordance rate of monozygotic twins with psoriasis is greater than that of dizygotic twins, with genetic thctors underpinning 66-90% of the variation in risk of developing psoriasis.

As described in previous work, the use of synthetic chemical ingredients in modern cosmetics is postulated to be a cause of damage to the skin microbiome. The discovery that biodiversity on the human skin is currently the only reliable indicator of skin health, meant that for the first time, a mechanism to test for healthy skin was possible. Using this mechanism and in collaboration with The Medical University of Graz, who carried out the independent study, this work aimed to help answer whether modern day synthetic cosmetics are a main cause of long-term damage to the skin microbiome. Thirty-two human participants tested three different face washes for their effect on the skin’s microbial diversity, along with skin pH, moisture and TEWL (trans-epidermal water loss), washing twice-a-day for four weeks. The upper volar forearm of the volunteers was swabbed at the beginning, two weeks in and at the end of the four weeks. 16S rRNA sequencing was used. One leading ‘natural’ brand full of synthetic ingredients, a leading synthetic brand and a 100% natural face wash were used. Results give the first indications of a link between synthetic ingredients in a cosmetics product and its effect on skin microbiome biodiversity. It paves the way for future studies on the topic with a larger sample group, longer test period and standardised methodology to create a universal standard for testing the health of skin using benchmark diversity values. This can be used in the future to test the effectiveness of cosmetics or ingredients on skin health, leading to the restriction in cosmetics of products proven to harm the skin’s natural environment.

We propose a set of criteria for topical probiotics to adhere to for safe and effective use for the skin microbiome. To form the basis of the criteria, we redefine the term “probiotics” and discuss successful and unsuccessful high-profile examples of the artificial addition of organisms to ecosystems in nature to understand what worked and what did not. Probiotics are often immediately assumed to have health benefits. However, as ecologists are aware, interfering with ecosystems is potentially catastrophic. The addition or removal of just one organism can significantly upset the delicate ecosystem balance. If our criteria are not met, we argue that topical probiotics could also cause damage and will not be beneficial. Due to the large intra- and inter-personal variation of the skin microbiome, our current knowledge of a healthy skin microbiome composition is not complete enough to fully satisfy the criteria. In follow-up work, we will investigate whether current topical probiotics research and commercial products meet our new criteria. We will also discuss problems with how to measure their effectiveness and suggest alternative solutions to replacing the lost biodiversity of the skin microbiome that was stripped away by environmental factors in the Western world.