Dandruff is associated with the conjoined interactions between host and microorganisms

Perturbations in the skin microbiome of infantile and adult seborrheic dermatitis and new treatment options based on restoring a healthy skin microbiome

Seborrheic dermatitis (SD) is a common, multifaceted skin condition, but its undefined etiology hampers the development of effective therapeutic strategies. In this review, we describe the intricate relationship between the skin microbiome and the pathogenesis of SD, focusing on the complex interplay between three major groups of organisms that can either induce inflammation (Malassezia spp., Staphylococcus aureus) or else promote healthy skin (Propionibacterium spp.). We describe how the disequilibrium of these microorganisms in the skin microbiome can develop skin inflammation in SD patients. Understanding these complex interactions of the skin microbiome has led to development of novel probiotics (e.g., Vitreoscilla spp. and Lactobacillus spp.) to restore normal skin physiology in SD. There are also differences in the skin microbiomes of healthy and SD infant and adult patients that impact pathogenesis and prompt different management strategies. A deeper understanding of the skin microbiome and its dynamic interactions will provide valuable insights into the pathogenesis of SD and prompt further development of targeted probiotic treatments to restore the balance of the skin microbiome in SD patients.

New Frontiers of Non-Invasive Detection in Scalp and Hair Diseases: A Review of the Application of Novel Detection Techniques

OBJECTIVE

The aim of this paper is to review the current status and recent progress of the application of novel non-invasive testing technologies in the diagnosis, treatment, and care of scalp hair diseases in recent years, and to discuss their contribution to the improvement of scalp hair health management.

METHODS

Through a literature review, the principles and current status of application of technologies such as trichoscopy, microbiological testing, scalp skin physiological function testing, hair physiological index testing, and hair product patch testing, and their specific roles in the management of scalp hair diseases were systematically sorted out.

RESULTS

Trichoscopic intelligent analysis technology can quantitatively assess the hair growth status and provide an objective assessment of the efficacy of hair diseases; microbiological testing provides a laboratory reference for the rapid diagnosis of scalp diseases and clinical use of medication; scalp skin physiological function testing and hair physiological index testing are essential for a comprehensive assessment of the scalp environment and hair health. The patch test can effectively detect allergenic substances, which can help to safely select topical drugs and hair care products, avoid medical risks, and facilitate safety evaluation.

CONCLUSION

Novel non-invasive testing techniques provide powerful technical support for accurate diagnosis, personalized treatment, and safe care of scalp hair diseases, and show a broad application prospect. Future research should focus on improving the accuracy and detection efficiency of these techniques to meet the growing demand for scalp hair health management and to promote the development of this field in a more scientific and refined direction.

Ribotyping Staphylococcus epidermidis Using Probabilistic Sequence Analysis and Levenshtein Distance Algorithm

Staphylococcus epidermidis (S. epidermidis) live in different human locations and natural environments. For ribotyping S. epidermidis sub-species, 2507 PCR-amplified reads of 16S rRNA genes of S. epidermidis in a public dataset were used for probabilistic sequence analysis. A sequence probability logo (sequence pLogo) as a reference sequence of 16S rRNA genes of S. epidermidis was constructed. Through implementation of Levenshtein Distance algorithm, two 20-base pairs (bp) motifs, commonly present in 2507 PCR-amplified reads, were identified. The top 38 S. epidermidis isolates, which carried 16S rRNA nucleotide domains that were made of different sequences but have high similarity scores to two 20-bp motifs, were found from 11 human, 8 animal, 9 plant and 10 environmental samples, indicating that these two 20-bp motifs were broadly present in diverse S. epidermidis isolates. Thirty-one PCR-amplified reads of 16S rRNA genes, which were currently not in the dataset, were utilized to verify the feasibility of using two 20-bp motifs for ribotyping S. epidermidis sub-species. S. epidermidis S1, S3, but not S2, isolates on the human scalp carried a 20-bp sequence domain with high similarities to a 20-bp motif in the sequence pLogo. The phylogenetic tree showed that S. epidermidis S1, S2 and S3 were not from a single common ancestor. Two newly identified 20-bp motifs here, thus, provided reference nucleotide residues for ribotyping S. epidermidis.

The Disturbed Microbial Niches of Itchy Scalp

BACKGROUND

Scalp itch without evident cause is an uncomfortable symptom that annoys many people in life but lacks adequate attention in academic.

AIMS

To investigate the relationship between scalp itching and microorganisms, and identify the key microbes and predicted functions associated with scalp itching, furtherly to provide useful targets for scalp itch solution.

METHODS

We performed microbial comparison between 44 normal subjects and 89 subjects having scalp itching problem with un-identified origin based on 16S rRNA gene sequencing and ddPCR (digital droplet PCR), and identified itch relevant microbes and predicted functions. To minimize false positive findings, another 43 itchy subjects were used for independent validation.

RESULTS

The three most abundant bacterial genus Cutibacterium, Lawsonella, Staphylococcus and predominant fungi Malassezia were not significantly different between the normal and itchy subjects, but an imbalance between Cutibacterium and Staphylococcus occurred in itchy scalp. As the predominant function contributor in the community, various Cutibacterium ASVs (amplicon sequence variants) were detected in itchy or normal subjects with low abundance and were subject specific. Some non-resident microbes from environment such as Leptolyngbya ANT.L52.2 and Pseudomonas were enhanced in itchy scalp and occupied an important ecological niche. The severity of itch was alleviated when these low abundant and low subject coverage ASVs were reduced or diminished.

CONCLUSIONS

Our findings raise the attention to (1) the ratio of Cutibacterium to Staphylococcus and (2) the low abundant bacteria on scalp, and provide potential solutions to ease scalp itch.

Unveiling the hidden causal links: skin flora and cutaneous melanoma

Objective

The presence of skin flora (SF) has been identified as a significant factor in the onset and progression of cutaneous melanoma (CM). However, the vast diversity and abundance of SF present challenges to fully understanding the causal relationship between SF and CM.

Methods

A Two Sample Mendelian Randomization (TSMR) analysis was conducted to investigating the causal relationship between SF and CM. The Inverse-Variance Weighted (IVW) method was utilized as the primary approach to assess the causal relationship under investigation. Furthermore, an independent external cohort was employed to validate the initial findings, followed by a meta-analysis of the consolidated results. To address potential confounding factors related to the influence of SF on CM, a Multivariate Mendelian Randomization (MVMR) analysis was also conducted. Finally, a Reverse Mendelian Randomization (RMR) was conducted to further validate the causal association.

Results

TSMR results showed that 9 SF have a causal relationship with CM in the training cohort. Although these 9 SF weren't confirmed in the testing cohort, 4 SF remained significant in the meta-analysis after integrating results from both cohorts. MVMR analysis indicated that 3 SF were still significantly associated with CM after accounting for the interactions between different SF in the training cohort. No reverse causal relationship was identified in RMR analysis.

Conclusion

A total of 9 SF were identified as having a potential causal relationship with CM; however, a large randomized controlled trial is needed to verify these results.

Aging-Induced Changes in Cutibacterium acnes and Their Effects on Skin Elasticity and Wrinkle Formation

Skin aging involves biomechanical changes like decreased elasticity, increased wrinkle formation, and altered barrier function. The skin microbiome significantly impacts this process. Here, we investigated the effects of decreased Cutibacterium acnes abundance and increase in other skin microorganisms on skin biomechanical properties in 60 healthy Koreans from Seoul, divided into younger (20-29 years) and older (60-75 years) groups. Metagenomic sequencing and skin assessments showed that the older group exhibited decreased C. acnes dominance and increased microbial diversity, correlating with reduced skin elasticity and increased wrinkles. In the younger age group, the enriched pathways included zeatin biosynthesis, distinct biotin metabolism pathways, and cofactor and vitamin metabolism in the younger age group, whereas pathways related to lipid metabolism, energy metabolism, and responses to environmental stressors, including UV damage and pollution, were enriched in the older group, according to functional analysis results. Network analysis indicated higher microbial connectivity in the younger group, suggesting a more stable community, whereas the older group's community displayed higher modularity, indicating more independent and specialized clusters. This study enhances our understanding of the impact of skin microbiome changes on skin aging, particularly the anti-aging effects of C. acnes. Future research should focus on the physiological mechanisms of skin microbiota on skin aging and explore therapeutic potentials to enhance skin health.

Investigation of the fermentation filtrate from soapberry (Sapindus mukorossi Gaertn.) pericarp on improving the microbial diversity and composition of the human scalp

Introduction

Microorganisms as a component of scalp ecosystem play a vital role in human scalp health. Soapberry pericarp is employed in improving scalp health, and its content of active ingredients could be enhanced resulted in fermentation. This study aims to investigate the effect of the fermentation filtrate from soapberry pericarp on the diversity of scalp microorganisms.

Methods

The components in fermentation filtrate from soapberry pericarp were analyzed by HPLC-Q-Orbitrap HRMS, and 16S and ITS sequences of 198 samples from three different used stages (Day 0, Day 7, Day 28) were sequenced using the Illumina Novaseq platform. Microbial diversity was assessed using alpha diversity (Chao1 and Shannon indexes) and beta diversity (weighted unifrac and unweighted unifrac). Principal coordinate analysis (PCoA) and linear discriminant analysis (LDA) effect size analysis (LEfSe) were used to visualize microbial variation among different stages.

Results

There were 22 components were identified in the fermentation filtrate from soapberry pericarp by HPLC-Q-Orbitrap HRMS. The alpha-diversity and beta-diversity analyses showed that scalp microbial diversity and composition were influenced by the fermentation filtrate of soapberry pericarp. Based on functional analysis, this study found an enrichment of healthy scalp-related bacterial pathways, such as amino acid, nucleoside, and nucleotide biosynthesis, while a decrease in fungal pathogenesis pathways, specifically saprotroph and symbiotroph pathways, was observed.

Discussion

The study described about the complex community dynamics of human scalp microorganisms during the stages of using the fermentation filtrate from soapberry pericarp. This result will help rationally utilize the fermentation filtrate from soapberry pericarp to keep or improve human scalp health.

Sample collecting methods for bacterial community structure analysis of scalp hair: non-invasive swabbing versus intrusive hair shaft cutting

Human skin samples for microbiome analysis are traditionally collected using a non-invasive swabbing method. Here, we compared the differences in bacterial community structures on scalp hair and scalps with samples collected using non-invasive swabbing and cutting/removal of scalp hair in 12 individuals. Hair-related samples, such as hair shafts and hair swabs, had significantly higher alpha diversity than scalp swab samples, whereas there were no significant differences between hair shafts and hair swabs. The relative abundances of the three major phyla and five major operational taxonomic units were not significantly different between the hair shaft and hair swab samples. The principal coordinate analysis plots based on weighted UniFrac distances were grouped into two clusters: samples from hair-related areas and scalp swabs, and there were significant differences only between samples from hair-related areas and scalp swabs. In addition, a weighted UniFrac analysis revealed that the sampling site-based category was a statistical category but not a hair sampling method-based category. These results suggest that scalp hair bacteria collected using non-invasive swab sampling were comparable to those collected cutting/removal of scalp hair.

Plant Phenolics in the Prevention and Therapy of Acne: A Comprehensive Review

Plants are a rich source of secondary metabolites, among which phenolics are the most abundant. To date, over 8000 various polyphenolic compounds have been identified in plant species, among which phenolic acids, flavonoids, coumarins, stilbenes and lignans are the most important ones. Acne is one of the most commonly treated dermatological diseases, among which acne vulgaris and rosacea are the most frequently diagnosed. In the scientific literature, there is a lack of a detailed scientific presentation and discussion on the importance of plant phenolics in the treatment of the most common specific skin diseases, e.g., acne. Therefore, the aim of this review is to gather, present and discuss the current state of knowledge on the activity of various plant phenolics towards the prevention and treatment of acne, including in vitro, in vivo and human studies. It was revealed that because of their significant antibacterial, anti-inflammatory and antioxidant activities, phenolic compounds may be used in the treatment of various types of acne, individually as well as in combination with commonly used drugs like clindamycin and benzoyl peroxide. Among the various phenolics that have been tested, EGCG, quercetin and nobiletin seem to be the most promising ones; however, more studies, especially clinical trials, are needed to fully evaluate their efficacy in treating acne.

Comparison of the Skin Microbiota in the Periocular Region between Patients with Inflammatory Skin Diseases and Healthy Participants: A Preliminary Study

(1) Background: Periocular or periorbital dermatitis is a common term for all inflammatory skin diseases affecting the area of skin around the eyes. The clear etiopathogenesis of periocular dermatitis is still not fully understood. Advances in molecular techniques for studying microorganisms living in and on our bodies have highlighted the microbiome as a possible contributor to disease, as well as a promising diagnostic marker and target for innovative treatments. The aim of this study was to compare the composition and diversity of the skin microbiota in the periocular region between healthy individuals and individuals affected by the specific entity of periocular dermatitis. (2) Methods: A total of 35 patients with periocular dermatitis and 39 healthy controls were enrolled in the study. After a skin swab from the periocular region was taken from all participants, DNA extraction and 16S rRNA gene amplicon sequencing using Illumina NovaSeq technology were performed. (3) Results: Staphylococcus and Corynebacterium were the most abundant bacterial genera in the microbiota of healthy skin. Analysis of alpha diversity revealed a statistically significant change (p < 0.05) in biodiversity based on the Faith's PD index between patients and healthy individuals. We did not observe changes in beta diversity. The linear discriminant analysis effect size (LEfSe) revealed that Rothia, Corynebacterium, Bartonella, and Paracoccus were enriched in patients, and Anaerococcus, Bacteroides, Porphyromonas, and Enhydrobacter were enriched in healthy controls. (4) Conclusions: According to the results obtained, we assume that the observed changes in the bacterial microbiota on the skin, particularly Gram-positive anaerobic cocci and skin commensals of the genus Corynebacterium, could be one of the factors in the pathogenesis of the investigated inflammatory diseases. The identified differences in the microbiota between healthy individuals and patients with periocular dermatitis should be further investigated.

Probiotics in Dermatology: An Evidence-based Approach

Probiotics are viable microorganisms that confer health benefits when administered to the host in adequate amounts. Over the past decade, there has been a growing demand for the use of oral and topical probiotics in several inflammatory conditions such as atopic dermatitis, psoriasis, acne vulgaris, etc., although their role in a few areas still remains controversial. The objective of this article is to shed light on understanding the origin and implications of microbiota in the pathophysiology of these dermatological conditions and the effect of probiotic usage. We have conducted a comprehensive search of the literature across multiple databases (PubMed, EMBASE, MEDLINE, and Google Scholar) on the role of probiotics in dermatological disorders. Commensal microbes of the skin and gastrointestinal tract play an important role in both health and disease. Increased use of probiotics has asserted a good safety profile, especially in this era of antibiotic resistance. With the advent of new products in the market, the indications, mechanism of action, efficacy, and safety profile of these agents need to be validated. Further studies are required. Oral and topical probiotics may be tried as a treatment or prevention modality in cutaneous inflammatory disorders, thus facilitating decreased requirement for topical or systemic steroids and antimicrobial agents. Tempering microbiota with probiotics is a safe and well-tolerated approach in this era of antimicrobial resistance.

Investigation of piroctone olamine delivery to the skin from single, binary and ternary solvent systems

OBJECTIVE

Disruption of the protective stratum corneum barrier increases the skin's vulnerability to microorganisms and facilitates conditions such as dandruff. Dandruff is a disorder of the scalp that causes increased scaling of the SC and is associated with Malassezia fungus. Consequently, many anti-dandruff commercial products use anti-fungal active ingredients such as piroctone olamine also known as Octopirox (OPX). OPX is an active ingredient used in a number of topical preparations for the management of dandruff. The characterization of the physicochemical properties of OPX was previously reported. The aim of the present work was to investigate a range of solvent systems for their effects on OPX interaction with human skin.

METHODS

The solvents used in this study were propylene glycol (PG), diethylene glycol monoethyl ether or Transcutol® (TC), PG monolaurate (PGML), isopropyl myristate (IPM), caprylic/capric triglyceride or Labrafac™ Lipophile WL 1349 (LAB), PG caprylate or Capryol® 90 (CAP), isostearyl isostearate (ISIS) and Plurol® Oleique CC 497 (PIOI). The single solvent systems evaluated were PG, TC, PGML, IPM, ISIS and CAP. For the binary solvent systems, PG and TC were examined. Ternary solvent systems consisted of: PG, TC and LAB; PG, PGML and LAB; and PG, TC and IPM. The concentration of OPX used was 1% (w/v). Heat-separated human epidermis was used for 24 h permeation experiments performed under finite dose conditions; mass balance studies were also conducted.

RESULTS

For the six single solvents examined no permeation was evident. Skin permeation of OPX was observed for binary and ternary solvent systems. The highest permeation for all PG:TC binary solvent system ratios tested was from the PG:TC (75:25) system. For the ternary solvent systems investigated, highest cumulative permeation of OPX was observed for PG:PGML:LAB (60:30:10). Considering all systems, PG:TC (75:25) delivered the greatest amount of OPX through the skin. Although OPX is deposited in the skin following the application of neat solvents, higher skin retention values were generally observed for binary and ternary systems.

CONCLUSION

To our knowledge, this is the first study to examine the permeation behaviour of OPX for a range of single, binary and ternary solvent systems.

Characterization of distinct microbiota associated with androgenetic alopecia patients treated and untreated with platelet-rich plasma (PRP)

BACKGROUND

Androgenic alopecia (AGA) is the most common type of hair loss in men, and there are many studies on the treatment of hair loss by platelet-rich plasma (PRP). The human scalp contains a huge microbiome, but its role in the process of hair loss remains unclear, and the relationship between PRP and the microbiome needs further study. Therefore, the purpose of this study was to investigate the effect of PRP treatment on scalp microbiota composition.

METHODS

We performed PRP treatment on 14 patients with AGA, observed their clinical efficacy, and collected scalp swab samples before and after treatment. The scalp microflora of AGA patients before and after treatment was characterized by amplifying the V3-V4 region of the 16 s RNA gene and sequencing for bacterial identification.

RESULTS

The results showed that PRP was effective in the treatment of AGA patients, and the hair growth increased significantly. The results of relative abundance analysis of microbiota showed that after treatment, g_Cutibacterium increased and g_Staphylococcus decreased, which played a stable role in scalp microbiota. In addition, g_Lawsonella decreased, indicating that the scalp oil production decreased after treatment.

CONCLUSIONS

The findings suggest that PRP may play a role in treating AGA through scalp microbiome rebalancing.

More yeast, more problems?: reevaluating the role of Malassezia in seborrheic dermatitis

Seborrheic dermatitis (SD) is an inflammatory skin disorder and eczema subtype increasingly recognized to be associated with significant physical, psychosocial, and financial burden. The full spectrum of SD, including dandruff localized to the scalp, is estimated to affect half of the world's population. Despite such high prevalence, the exact etiopathogenesis of SD remains unclear. Historically, many researchers have theorized a central, causative role of Malassezia spp. based on prior studies including the proliferation of Malassezia yeast on lesional skin of some SD patients and empiric clinical response to antifungal therapy. However, upon closer examination, many of these findings have not been reproducible nor consistent. Emerging data from novel, targeted anti-inflammatory therapeutics, as well as evidence from genome-wide association studies and murine models, should prompt a reevaluation of the popular yeast-centered hypothesis. Here, through focused review of the literature, including laboratory studies, clinical trials, and expert consensus, we examine and synthesize the data arguing for and against a primary role for Malassezia in SD. We propose an expansion of SD pathogenesis and suggest reframing our view of SD to be based primarily on dysregulation of the host immune system and skin epidermal barrier, like other eczemas.

Microbiome: Role in Inflammatory Skin Diseases

As the body's largest organ, the skin harbors a highly diverse microbiota, playing a crucial role in resisting foreign pathogens, nurturing the immune system, and metabolizing natural products. The dysregulation of human skin microbiota is implicated in immune dysregulation and inflammatory responses. This review delineates the microbial alterations and immune dysregulation features in common Inflammatory Skin Diseases (ISDs) such as psoriasis, rosacea, atopic dermatitis(AD), seborrheic dermatitis(SD), diaper dermatitis(DD), and Malassezia folliculitis(MF).The skin microbiota, a complex and evolving community, undergoes changes in composition and function that can compromise the skin microbial barrier. These alterations induce water loss and abnormal lipid metabolism, contributing to the onset of ISDs. Additionally, microorganisms release toxins, like Staphylococcus aureus secreted α toxins and proteases, which may dissolve the stratum corneum, impairing skin barrier function and allowing entry into the bloodstream. Microbes entering the bloodstream activate molecular signals, leading to immune disorders and subsequent skin inflammatory responses. For instance, Malassezia stimulates dendritic cells(DCs) to release IL-12 and IL-23, differentiating into a Th17 cell population and producing proinflammatory mediators such as IL-17, IL-22, TNF-α, and IFN-α.This review offers new insights into the role of the human skin microbiota in ISDs, paving the way for future skin microbiome-specific targeted therapies.

Modulating the skin mycobiome-bacteriome and treating seborrheic dermatitis with a probiotic-enriched oily suspension

Seborrheic dermatitis (SD) affects 2-5% of the global population, with imbalances in the skin microbiome implicated in its development. This study assessed the impact of an oily suspension containing Lactobacillus crispatus P17631 and Lacticaseibacillus paracasei I1688 (termed EUTOPLAC) on SD symptoms and the skin mycobiome-bacteriome modulation. 25 SD patients were treated with EUTOPLAC for a week. Symptom severity and skin mycobiome-bacteriome changes were measured at the start of the treatment (T0), after seven days (T8), and three weeks post-treatment (T28). Results indicated symptom improvement post-EUTOPLAC, with notable reductions in the Malassezia genus. Concurrently, bacterial shifts were observed, including a decrease in Staphylococcus and an increase in Lactobacillus and Lacticaseibacillus. Network analysis highlighted post-EUTOPLAC instability in fungal and bacterial interactions, with increased negative correlations between Malassezia and Lactobacillus and Lacticaseibacillus genera. The study suggests EUTOPLAC's potential as a targeted SD treatment, reducing symptoms and modulating the mycobiome-bacteriome composition.

Part 1: Understanding the role of Malassezia spp. in skin disorders: Malassezia yeasts as commensal or pathogenic organisms of human and animal skin

INTRODUCTION

Malassezia spp. are a group of lipid-dependent basidiomycetes yeasts acting as commensal organisms of the human and animal skin. However, under some not well-defined circumstances, these yeasts may switch to opportunistic pathogens triggering a number of skin disorders with different clinical presentations. The genus comprises of 18 lipid-dependent species with a variable distribution in the hosts and pathologies thus suggesting a host- and microbe-specific interactions.

AREA COVERED

This review highlighted and discussed the most recent literature regarding the genus Malassezia as a commensal or pathogenic organisms highlighting Malassezia-associated skin disorders in humans and animals and their antifungal susceptibility profile. A literature search of Malassezia associated skin disorders was performed via PubMed and Google scholar (up to May 2023), using the different keywords mainly associated with Malassezia skin disorders and Malassezia antifungal resistance.

EXPERT OPINION

Malassezia yeasts are part of the skin mycobiota and their life cycle is strictly associated with the environment in which they live. The biochemical, physiological, or immunological condition of the host skin selects Malassezia spp. or genotypes able to survive in a specific environment by changing their metabolisms, thus producing virulence factors or metabolites which can cause skin disorders with different clinical presentations.

Compositional Variations between Adult and Infant Skin Microbiome: An Update

Human skin and its commensal microbiome form the first layer of protection to the outside world. A dynamic microbial ecosystem of bacteria, fungi and viruses, with the potential to respond to external insult, the skin microbiome has been shown to evolve over the life course with an alteration in taxonomic composition responding to altered microenvironmental conditions on human skin. This work sought to investigate the taxonomic, diversity and functional differences between infant and adult leg skin microbiomes. A 16S rRNA gene-based metataxonomic analysis revealed significant differences between the infant and adult skin groups, highlighting differential microbiome profiles at both the genus and species level. Diversity analysis reveals differences in the overall community structure and associated differential predicted functional profiles between the infant and adult skin microbiome suggest differing metabolic processes are present between the groups. These data add to the available information on the dynamic nature of skin microbiome during the life course and highlight the predicted differential microbial metabolic process that exists on infant and adult skin, which may have an impact on the future design and use of cosmetic products that are produced to work in consort with the skin microbiome.

Mechanisms of impairment in hair and scalp induced by hair dyeing and perming and potential interventions

With the rapid growth of beauty and personal care industries, many hair-relevant products, hair dyes and hair perms in particular, are increasingly prevalent in both women and men, regardless of being young or old as they frequently change hair color or shape to enhance youthfulness and beauty and to follow fashion trends. Hair dyes and perms alter hair color and/or shape by mechanically changing the physical structure and chemical substances of the hair shaft. However, treatment of hair with chemical formulations has been potentially ascribed to adverse outcomes in the hair shaft including structure damage, chemical constituent disorder, and impaired physical properties, although hair cosmetics procedures are intrinsically safe. Nevertheless, the mechanisms of impairment in the hair shaft and scalp induced by hair dyeing and perming remain elusive. Additionally, adverse reactions activated by exposure to specific chemical ingredients including skin irritation, allergic contact dermatitis (ACD), and even cancer risk have been reported clinically, but existing evidence is not consistent enough in the case of human studies. Herein, the review aims to give an overview of hair cosmetics, especially concerning the basic knowledge about various hair dyes and perms, the consequences for hair shafts and the scalp resulting from the application of hair cosmetics mentioned above, mechanisms of hazardous outcomes, and potential desirable interventions to alleviate the impairment.

Heat-killed Lacticaseibacillus paracasei GMNL-653 ameliorates human scalp health by regulating scalp microbiome

BACKGROUND

The equilibrium of the scalp microbiome is important for maintaining healthy scalp conditions, including sebum secretion, dandruff, and hair growth. Many different strategies to improve scalp health have been reported; however, the effect of postbiotics, such as heat-killed probiotics, on scalp health remains unclear. We examined the beneficial effects of heat-killed probiotics consisting of Lacticaseibacillus paracasei, GMNL-653, on scalp health.

RESULTS

Heat-killed GMNL-653 could co-aggregate with scalp commensal fungi, Malassezia furfur, in vitro, and the GMNL-653-derived lipoteichoic acid inhibited the biofilm formation of M. furfur on Hs68 fibroblast cells. The mRNA of hair follicle growth factors, including insulin-like growth factor-1 receptor (IGF-1R), vascular endothelial growth factor, IGF-1, and keratinocyte growth factor was up-regulated in skin-related human cell lines Hs68 and HaCaT after treatment with heat-killed GMNL-653. For clinical observations, we recruited 22 volunteer participants to use the shampoo containing the heat-killed GMNL-653 for 5 months and subsequently measured their scalp conditions, including sebum secretion, dandruff formation, and hair growth. We applied polymerase chain reaction (PCR) to detect the scalp microbiota of M. restricta, M. globosa, Cutibacterium acnes, and Staphylococcus epidermidis. A decrease in dandruff and oil secretion and an increase in hair growth in the human scalp were observed after the use of heat-killed GMNL-653-containing shampoo. The increased abundance of M. globosa and the decreased abundance of M. restricta and C. acnes were also observed. We further found that accumulated L. paracasei abundance was positively correlated with M. globosa abundance and negatively correlated with C. acnes abundance. S. epidermidis and C. acnes abundance was negatively correlated with M. globosa abundance and positively correlated with M. restricta. Meanwhile, M. globosa and M. restricta abundances were negatively associated with each other. C. acnes and S. epidermidis abundances were statistically positively correlated with sebum secretion and dandruff, respectively, in our shampoo clinical trial.

CONCLUSION

Our study provides a new strategy for human scalp health care using the heat-killed probiotics GMNL-653-containing shampoo. The mechanism may be correlated with the microbiota shift.

Seborrheic dermatitis: topical therapeutics and formulation design

Seborrheic dermatitis (SD) is a common dermatological disorder with symptoms that include skin flaking, erythema and pruritus. This review discusses the topical products available for treating SD, which target several aspects of disease pathobiology, including cutaneous microbial dysbiosis (driven by Malassezia yeast), inflammation, sebum production and skin barrier disruption. Among the various treatments available, zinc pyrithione (ZnPT) based products that exhibit anti-fungal action are the market leaders. A skin compartment approach is presented here for combining ZnPT exposure information with threshold levels for anti-fungal efficacy and toxicity, overall providing a comprehensive picture of ZnPT therapeutics and safety. While Malassezia yeast on the surface are effectively targeted, yeast residing beyond the superficial follicle may not receive adequate ZnPT for anti-fungal effect forming the basis for skin re-colonisation. Levels entering systemic circulation from topical delivery are well below toxic thresholds, however the elevated zinc levels within the viable epidermis warrants further investigation. Strategies to improve formulation design can be broadly classified as influencing 1) topical delivery, 2) therapeutic bioactivity, 3) skin mildness, and 4) sensory attributes. Successful SD treatment ultimately requires formulations that can balance efficacy, safety, and consumer appeal.

Alteration in skin mycobiome due to atopic dermatitis and seborrheic dermatitis

A microbiome consists of viruses, bacteria, archaea, fungi, and other microeukaryotes. It influences host immune systems and contributes to the development of various diseases, such as obesity, diabetes, asthma, and skin diseases, including atopic dermatitis and seborrheic dermatitis. The skin is the largest organ in the human body and has various microorganisms on its surface. Several studies on skin microbiomes have illustrated the effects of their composition, metabolites, and interactions with host cells on diseases. However, most studies have focused on the bacterial microbiome rather than the fungal microbiome, namely, mycobiome, although emerging evidence indicates that fungi also play a critical role in skin microbiomes through interactions with the host cells. I briefly summarize the current progress in the analysis of mycobiomes on human skin. I focused on alteration of the skin mycobiome caused by atopic and seborrheic dermatitis, with an emphasis on the Malassezia genus, which are the most dominant fungi residing here.

Staphylococcus epidermidis and its dual lifestyle in skin health and infection

The coagulase-negative bacterium Staphylococcus epidermidis is a member of the human skin microbiota. S. epidermidis is not merely a passive resident on skin but actively primes the cutaneous immune response, maintains skin homeostasis and prevents opportunistic pathogens from causing disease via colonization resistance. However, it is now appreciated that S. epidermidis and its interactions with the host exist on a spectrum of potential pathogenicity derived from its high strain-level heterogeneity. S. epidermidis is the most common cause of implant-associated infections and is a canonical opportunistic biofilm former. Additional emerging evidence suggests that some strains of S. epidermidis may contribute to the pathogenesis of common skin diseases. Here, we highlight new developments in our understanding of S. epidermidis strain diversity, skin colonization dynamics and its multifaceted interactions with the host and other members of the skin microbiota.

Acne Vulgaris, Atopic Dermatitis and Rosacea: The Role of the Skin Microbiota-A Review

The skin harbors a huge number of different microorganisms such as bacteria, fungi and viruses, and it acts as a protective shield to prevent the invasion of pathogens and to maintain the health of the commensal microbiota. Several studies, in fact, have shown the importance of the skin microbiota for healthy skin. However, this balance can be altered by intrinsic and extrinsic factors, leading to the development of skin disease, such as acne vulgaris (AV), atopic dermatitis (AD) and rosacea(RS). Although these diseases are widespread and affect both adolescents and adults, the scientific correlation between these disorders and the skin microbiota and physiological parameters (TEWL, hydration and lipid composition) is still unclear. This review aims to investigate the current literature regarding the correlation between the skin microbiota and its imbalance underlying microbiological aspects, how the skin microbiota changes over the course of the disease and the current possible treatments. The following reported studies show a general imbalance of the bacterial flora. For this reason, more in-depth studies are necessary to explore the different subspecies and strains involved in all three diseases.

Microbiota profiling on itchy scalp with undetermined origin

Scalp pruritus is a common skin problem that remains therapeutic challenge. The relationships between the dysbiosis of microbiota and skin diseases have caught attention recently. However, there are few reports about microbiota on itchy scalp. This study investigated scalp microbial characteristics of subjects with mild scalp pruritus of undetermined origin and preliminarily screened physiological factors and bacteria potentially related to pruritus. The pruritus severity of 17 qualified females was evaluated by Visual Analogue Scale (VAS). Microbiota collection was done at both itchy (n = 20) and non-itchy sites (n = 27) at occiput and crown of the same subject and Illumina sequencing was performed at the V3-V4 hypervariable regions of 16S rRNA. The corresponding sebum content, hydration, pH, trans-epidermal water loss, erythema index and porphyrin numbers were also measured by skin tester. We identified 3044 amplicon sequence variants from 821 genera. The itchy and non-itchy sites had different microbiota structures (p = 0.045, by multivariate analysis of variance), while there were large inter- and intra-individual variations. Both sites had Staphylococcus, Cutibacterium and Lawsonella as predominant genera, which were not significantly related to pruritus. The use of three genera Lactobacillus, Morganella and Pseudomonas, could well distinguish non-itchy from itchy groups, whereas different composition patterns existed inside each group. Our investigation indicated that though the bacterial community structure on itchy scalp was individual specific, there was difference between itchy and non-itchy sites. The study provides new insights into microbiota profiling on itchy scalp, which will help microbiota-targeted therapeutic experiment or products design for scalp pruritus.

Altered skin fungal and bacterial community compositions in tinea capitis

BACKGROUND

Tinea capitis is an infection of the scalp and hair shaft caused by dermatophytes that predominantly occurs in children. Skin fungal infections have been found to be associated with alterations in the overall bacterial and fungal communities. However, the scalp microbiome in tinea capitis have not been fully investigated.

OBJECTIVES

To investigate and compare the scalp bacterial and fungal microbiomes between children with tinea capitis and healthy children and between children and adults.

METHODS

Skin samples were collected from the scalp. Bacterial and fungal community compositions were analysed by amplification sequencing of the V3-V4 of 16S rDNA and ITS1-5F, respectively.

RESULTS

The predominant fungi detected using amplicon sequencing were consistent with the culture- or real-time PCR-positive pathogens in most samples. Children with tinea capitis had lower fungal and higher bacterial Shannon diversity than healthy children. A higher relative abundance of pathogenic fungi and significant alterations in the bacterial community in the lesional sites of tinea capitis than healthy scalps. Compared with adults, healthy children were characterised by higher Shannon diversities with significantly lower relative abundances of Malassezia and Cutibacterium and higher relative abundances of Candida and Streptococcus.

CONCLUSIONS

We demonstrated that tinea capitis was characterised by significant alterations in both fungal and bacterial communities and amplicon sequencing could be a complementary method for pathogen identification.

Clinical Translation of Microbiome Research in Alopecia Areata: A New Perspective?

The continuous research advances in the microbiome field is changing clinicians’ points of view about the involvement of the microbiome in human health and disease, including autoimmune diseases such as alopecia areata (AA). Both gut and cutaneous dysbiosis have been considered to play roles in alopecia areata. A new approach is currently possible owing also to the use of omic techniques for studying the role of the microbiome in the disease by the deep understanding of microorganisms involved in the dysbiosis as well as of the pathways involved. These findings suggest the possibility to adopt a topical approach using either cosmetics or medical devices, to modulate or control, for example, the growth of overexpressed species using specific bacteriocins or postbiotics or with pH control. This will favour at the same time the growth of beneficial bacteria which, in turn, can impact positively both the structure of the scalp ecosystem on the host’s response to internal and external offenders. This approach, together with a “systemic” one, via oral supplementation, diet, or faecal transplantation, makes a reliable translation of microbiome research in clinical practice and should be taken into consideration every time alopecia areata is considered by a clinician.

Amplicon-based sequencing and co-occurence network analysis reveals notable differences of microbial community structure in healthy and dandruff scalps

Background

Dandruff is a chronic, recurring, and common scalp problem that is caused by several etiopathogeneses with complex mechanisms. Management of this condition is typically achieved via antifungal therapies. However, the precise roles played by microbiota in the development of the condition have not been elucidated. Despite their omnipresence on human scalp little is known about the co-occurrence/co-exclusion network of cutaneous microbiota.

Results

We characterized the scalp and hair surface bacterial and fungal communities of 95 dandruff-afflicted and healthy individuals residing in China. The degree distributions of co-occurrence/co-exclusion network in fungi-bacteria and bacteria-bacteria were higher in the healthy group (P < 0.0001), whereas the betweenness values are higher in the dandruff group (P < 0.01). Meanwhile, the co-occurrence/co-exclusion network among fungi-fungi and fungi-bacteria showed that compared to the healthy group, the dandruff group had more positive links (P < 0.0001). In addition, we observed that Malassezia slooffiae, Malassezia japonica and Malassezia furfur, were more abundant in the dandruff group than in the healthy group. These microbiota were co-exclusion by either multiple bacterial genera or Malassezia sp. in healthy group. The lactic acid bacteria on the scalp and hair surface, especially the genera Lactobacillus and Lactococcus, exhibit a negative correlation with multiple bacterial genera on the scalp and hair surface. Lactobacillus plantarum and Pediococcus lactis isolated on the healthy human scalp can inhibit the growth of Staphylococcus epidermidis in vitro.

Conclusions

We showed that microbial networks on scalp and hair surface with dandruff were less integrated than their healthy counterparts, with lower node degree and more positive and stronger links which were deemed to be unstable and may be more susceptible to environmental fluctuations. Lactobacillus bacteria have extensive interactions with other bacteria or fungi in the scalp and hair surface micro-ecological network and can be used as targets for improving scalp health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08534-4.

Is cutaneous microbiota a player in disease pathogenesis? Comparison of cutaneous microbiota in psoriasis and seborrheic dermatitis with scalp involvement

BACKGROUND

Knowledge about cutaneous microbiota in psoriasis vulgaris and seborrheic dermatitis is limited, and a comparison of microbiota in the two diseases was not yet previously undertaken.

AIMS/OBJECTIVES

This study aimed to compare the scalp lesional and non-lesional microbiota in psoriasis vulgaris and seborrheic dermatitis with that in a healthy control group.

METHODS

Fifty samples were taken with sterile swabs from patients' and controls' scalps, and 16S rRNA gene sequencing analyses were performed.

RESULTS

Alpha and beta diversity analyses showed that bacterial load and diversity were significantly increased in psoriasis vulgaris and seborrheic dermatitis lesions compared to the controls. As phyla, Actinobacteria decreased and Firmicutes increased, while as genera, Propionibacterium decreased; Staphylococcus, Streptococcus, Aquabacterium, Neisseria and Azospirillum increased in lesions of both diseases. Specifically, Mycobacterium, Finegoldia, Haemophilus and Ezakiella increased in psoriasis vulgaris and Enhydrobacter, Micromonospora and Leptotrichia increased in seborrheic dermatitis lesions. Mycobacterium, Ezakiella and Peptoniphilus density were higher in psoriasis vulgaris compared to seborrheic dermatitis lesions. The bacterial diversity and load values of non-lesional scalp in psoriasis vulgaris and seborrheic dermatitis lay between those of lesional areas and controls.

LIMITATIONS

The small sample size is the main limitation of this study.

CONCLUSION

Higher bacterial diversity was detected in lesions of both psoriasis and seborrheic dermatitis compared to the controls, but similar alterations were observed when the two diseases were compared. Although these differences could be a result rather than a cause of the two diseases, there is a need to analyze all members of the microbiota and microbiota-host interactions.

The Human Skin Microbiome in Selected Cutaneous Diseases

The human skin harbors a wide variety of microbes that, together with their genetic information and host interactions, form the human skin microbiome. The role of the human microbiome in the development of various diseases has lately gained interest. According to several studies, changes in the cutaneous microbiota are involved in the pathophysiology of several dermatoses. A better delineation of the human microbiome and its interactions with the innate and adaptive immune systems could lead to a better understanding of these diseases, as well as the opportunity to achieve new therapeutic modalities. The present review centers on the most recent knowledge on skin microbiome and its participation in the pathogenesis of several skin disorders: atopic and seborrheic dermatitis, alopecia areata, psoriasis and acne.

Facial Acne: A Randomized, Double-Blind, Placebo-Controlled Study on the Clinical Efficacy of a Symbiotic Dietary Supplement

Introduction

Treatments other than topical and systemic antibiotics are needed to restore the dysbiosis correlated with acne onset and evolution. In this view, probiotics and botanical extracts could represent a valid adjunctive therapeutic approach. The purpose of this study was to test the efficacy of a dietary supplement containing probiotics (Bifidobacterium breve BR03 DSM 16604, Lacticaseibacillus casei LC03 DSM 27537, and Ligilactobacillus salivarius LS03 DSM 22776) and botanical extract (lupeol from Solanum melongena L. and Echinacea extract) in subjects with mild to moderate acne over an 8-week study period.

Methods

Monocentric, randomized, double-blind, four-arm, placebo-controlled clinical study involving 114 subjects.

Results

A significant (p < 0.05) effect on the number of superficial inflammatory lesions was reported over the study period in the subjects taking the study agent (group II) (−56.67%), the botanical extracts (group III) (−40.00%), and the probiotics (group IV) (−38.89%) versus placebo (−10.00%). A significant (p < 0.05) decrease in mean desquamation score, sebum secretion rate, and porphyrin mean count versus baseline was also reported, and the effect was most evident for group II. The analysis of log relative abundance after 4 and 8 weeks of treatment compared with baseline showed a significant (p < 0.01) decrease in Cutibacterium acnes and S. aureus, along with a contextually and significant (p < 0.05) increase in Staphylococcus epidermidis, especially in group II. No significant changes were reported for group I.

Conclusion

The results from this study suggest that the administration of the dietary supplement under study was effective, safe, and well tolerated in subjects with mild to moderate acne and could represent a promising optional complement for the treatment of inflammatory acne as well as for control of acne-prone skin.

Anti-inflammatory and Antimicrobial Activities of Fermented Ocimum sanctum Linn. Extracts Against Skin and Scalp Microorganisms

This study aimed to revealed anti-inflammatory and antimicrobial activities of fermented Ocimum sanctum Linn. (FE). The fermentation process with Lactobacillus plantarum was compared with the solvent extraction methods. Antimicrobial activity against the growth of Staphylococcus aureus , Staphylococcus epidermidis , Propionibacterium acnes , Candida albicans , and Malassezia furfur was investigated via broth dilution method. High performance thin layer chromatography was used to determine eugenol content. The anti-inflammation was investigated by means of nuclear factor kappa B (NF-κB) expression inhibition by Western blot analysis. FE yielded the highest amount (11.93% w/w), the highest eugenol content (39.3 ± 12.6% w/w), and the highest antimicrobial activities comparing to the extracts obtained from the solvent extractions. The fungal inhibition against M . furfur 656 was equivalent to that of ketoconazole. Furthermore, the bacterial inhibition on S. aureus and S. epidermidis was compared to that of Penicillin G at minimum inhibitory concentration (MIC) of 0.125 mg/mL and 0.25 mg/mL, respectively. Interestingly, FE had lower MIC and minimum bactericidal concentration against P. acnes than Penicillin G and also possessed comparable anti-inflammatory activity to indomethacin with the NF-κB suppression of 42.7 ± 4.6%. Therefore, FE are potentially natural anti-inflammation and antimicrobial agents for topical applications in the pharmaceutical and cosmetic industries.

Evaluation of a new-formula shampoo containing 6% glycyrrhetinic acid complex for scalp seborrheic dermatitis: A pilot study

Background

Scalp seborrheic dermatitis (SD) is a chronic inflammatory dermatosis associated with sebum imbalance and proliferation of Malassezia species. Various antifungal shampoos are commonly used for scalp SD.

Aims

Glycyrrhetinic acid is known to have antioxidative, anti‐inflammatory, and anti‐allergic effects. This study was designed to evaluate the effectiveness of a new‐formula shampoo that contains glycyrrhetinic acid for the treatment of scalp SD.

Patients/Methods

Thirty‐four patients were enrolled and treated with the 6% glycyrrhetinic acid complex shampoo. Efficacy was assessed clinically with Dermatology Life Quality Index (DLQI) and Adherent Scalp Flaking Score (ASFS) by the same dermatologist at baseline, week 2, and week 5. Among the 24 subjects with the most significant clinical improvement, four common microorganisms from scalp samples were analyzed by quantitative polymerase chain reaction (qPCR) at baseline, and week 5.

Results

The DLQI and ASFS at week 2 and week 5 improved significantly relative to baseline. The bacteria profiles showed a significant increase of Cutibacterium acnes and a decrease of Staphylococcus epidermidis at week 5. The fungi profiles showed significant decreases of both Malassezia restricta and Malassezia globosa. The ratio of C. acne to S. epidermidis increased significantly from 0.93 at baseline to 1.55 at week 5. The ratio of M. restricta to M. globosa decreased from 5.02 at baseline to 1.00 at week 5.

Conclusions

The effectiveness of this new regimen was objectively demonstrated at the clinical and microbiological levels. This new formula may alleviate the bacterial and fungal dysbiosis in scalp SD.

Scalp Microbiome and Sebum Composition in Japanese Male Individuals with and without Androgenetic Alopecia

The skin microbiome and sebum may be associated with inflammation-related diseases of the scalp. To assess the pathogenesis and progression of androgenetic alopecia (AGA), we analyzed the composition of sebum and the bacterial and fungal microbiomes of the scalps of 118 Japanese male individuals with and without AGA, then discussed their roles in the pathogenesis of AGA. Sebum triglyceride and palmitic acid contents were higher in the AGA group than in the non-AGA group. Malassezia restricta, a lipophilic fungus that consumes palmitic acid, was abundant on the scalps of patients with AGA. Cutibacterium, Corynebacterium, and Staphylococcus were the most common genera in both groups, and patients with AGA exhibited scalp dysbiosis (increased abundance of Cutibacterium and decreased abundance of Corynebacterium). Our findings suggest that both sebum and the bacterial and fungal microbiomes of the scalp may be involved in the development of AGA.

Features of the Skin Microbiota in Common Inflammatory Skin Diseases

Many relatively common chronic inflammatory skin diseases manifest on the face (seborrheic dermatitis, rosacea, acne, perioral/periorificial dermatitis, periocular dermatitis, etc.), thereby significantly impairing patient appearance and quality of life. Given the yet unexplained pathogenesis and numerous factors involved, these diseases often present therapeutic challenges. The term “microbiome” comprises the totality of microorganisms (microbiota), their genomes, and environmental factors in a particular environment. Changes in human skin microbiota composition and/or functionality are believed to trigger immune dysregulation, and consequently an inflammatory response, thereby playing a potentially significant role in the clinical manifestations and treatment of these diseases. Although cultivation methods have traditionally been used in studies of bacterial microbiome species, a large number of bacterial strains cannot be grown in the laboratory. Since standard culture-dependent methods detect fewer than 1% of all bacterial species, a metagenomic approach could be used to detect bacteria that cannot be cultivated. The skin microbiome exhibits spatial distribution associated with the microenvironment (sebaceous, moist, and dry areas). However, although disturbance of the skin microbiome can lead to a number of pathological conditions and diseases, it is still not clear whether skin diseases result from change in the microbiome or cause such a change. Thus far, the skin microbiome has been studied in atopic dermatitis, seborrheic dermatitis, psoriasis, acne, and rosacea. Studies on the possible association between changes in the microbiome and their association with skin diseases have improved the understanding of disease development, diagnostics, and therapeutics. The identification of the bacterial markers associated with particular inflammatory skin diseases would significantly accelerate the diagnostics and reduce treatment costs. Microbiota research and determination could facilitate the identification of potential causes of skin diseases that cannot be detected by simpler methods, thereby contributing to the design and development of more effective therapies.

A Journey on the Skin Microbiome: Pitfalls and Opportunities

The human skin microbiota is essential for maintaining homeostasis and ensuring barrier functions. Over the years, the characterization of its composition and taxonomic diversity has reached outstanding goals, with more than 10 million bacterial genes collected and cataloged. Nevertheless, the study of the skin microbiota presents specific challenges that need to be addressed in study design. Benchmarking procedures and reproducible and robust analysis workflows for increasing comparability among studies are required. For various reasons and because of specific technical problems, these issues have been investigated in gut microbiota studies, but they have been largely overlooked for skin microbiota. After a short description of the skin microbiota, the review tackles methodological aspects and their pitfalls, covering NGS approaches and high throughput culture-based techniques. Recent insights into the "core" and "transient" types of skin microbiota and how the manipulation of these communities can prevent or combat skin diseases are also covered. Finally, this review includes an overview of the main dermatological diseases, the changes in the microbiota composition associated with them, and the recommended skin sampling procedures. The last section focuses on topical and oral probiotics to improve and maintain skin health, considering their possible applications for skin diseases.

Targeted Delivery of Zinc Pyrithione to Skin Epithelia

Zinc pyrithione (ZnPT) is an anti-fungal drug delivered as a microparticle to skin epithelia. It is one of the most widely used ingredients worldwide in medicated shampoo for treating dandruff and seborrheic dermatitis (SD), a disorder with symptoms that include skin flaking, erythema and pruritus. SD is a multi-factorial disease driven by microbiol dysbiosis, primarily involving Malassezia yeast. Anti-fungal activity of ZnPT depends on the cutaneous availability of bioactive monomeric molecular species, occurring upon particle dissolution. The success of ZnPT as a topical therapeutic is underscored by the way it balances treatment efficacy with formulation safety. This review demonstrates how ZnPT achieves this balance, by integrating the current understanding of SD pathogenesis with an up-to-date analysis of ZnPT pharmacology, therapeutics and toxicology. ZnPT has anti-fungal activity with an average in vitro minimum inhibitory concentration of 10-15 ppm against the most abundant scalp skin Malassezia species (Malassezia globosa and Malassezia restrica). Efficacy is dependent on the targeted delivery of ZnPT to the skin sites where these yeasts reside, including the scalp surface and hair follicle infundibulum. Imaging and quantitative analysis tools have been fundamental for critically evaluating the therapeutic performance and safety of topical ZnPT formulations. Toxicologic investigations have focused on understanding the risk of local and systemic adverse effects following exposure from percutaneous penetration. Future research is expected to yield further advances in ZnPT formulations for SD and also include re-purposing towards a range of other dermatologic applications, which is likely to have significant clinical impact.

A folliculocentric perspective of dandruff pathogenesis: Could a troublesome condition be caused by changes to a natural secretory mechanism?

Dandruff is a common scalp condition, which frequently causes psychological distress in those affected. Dandruff is considered to be caused by an interplay of several factors. However, the pathogenesis of dandruff remains under-investigated, especially with respect to the contribution of the hair follicle. As the hair follicle exhibits unique immune-modulatory properties, including the creation of an immunoinhibitory, immune-privileged milieu, we propose a novel hypothesis taking into account the role of the hair follicle. We hypothesize that the changes and imbalance of yeast and bacterial species, along with increasing proinflammatory sebum by-products, leads to the activation of immune response and inflammation. Hair follicle keratinocytes may then detect these changes in scalp microbiota resulting in the recruitment of leukocytes to the inflammation site. These changes in the scalp skin immune-microenvironment may impact hair follicle immune privilege status, which opens new avenues into exploring the role of the hair follicle in dandruff pathogenesis. Also see the video abstract here: https://youtu.be/mEZEznCYtNs.

Host factors that shape the bacterial community structure on scalp hair shaft

In this study, we performed 16S rRNA amplicon sequencing analysis of scalp hair shaft from 109 volunteers, who were surveyed using a questionnaire about daily scalp hair care, and employed multiple statistical analyses to elucidate the factors that contribute to the formation of bacterial community structures on scalp hair shaft. Scalp hair microbiota were found to be specific for each individual. Their microbiota were clearly divided into two clusters. Genus level richness of Pseudomonas (Ps) and Cutibacterium (Cu) contributed to the clusters. The clusters around Pseudomonas and Cutibacterium were named Ps-type and Cu-type, respectively. The host gender influenced the bacterial cell numbers of the major genera that included Cutibacterium, Lawsonella, Moraxella, and Staphylococcus on scalp hair shaft. In addition to host intrinsic factors, extrinsic factors such as hair styling and colouring affected the bacterial cell numbers of the major genera. These factors and chemical treatments, such as bleaching and perming, also affected the Ps-type to Cu-type ratios. These results suggest that bacterial community structures on scalp hair shaft are influenced by both intrinsic and extrinsic factors.

Skin microbiome alterations in seborrheic dermatitis and dandruff: A systematic review

Seborrheic dermatitis (SD) and dandruff (DF) are common chronic inflammatory skin diseases characterized by recurrent greasy scales, sometimes with erythema and itchiness. Although the exact pathophysiology of the disease is still unclear, current theories highlight the role of microbes on the skin surface in the pathogenesis of SD. Here, we conducted a systematic review to investigate the skin microbiome alterations in patients with SD/DF. We searched Medline/PubMed, Embase and Web of Science for research studies published in English between 1 January 2000 and 31 December 2020. A total of 12 studies with 706 SD/DF samples and 379 healthy samples were included in this study. The scalp and face were predominated by the fungi of Ascomycota and Basidiomycota and the bacteria of Actinobacteria and Firmicutes. In general, the included studies demonstrated an increased Malassezia restricta/Malassezia globosa ratio and a reduction in the Cutibaterium/Staphylococcus ratio in the setting of SD/DF. Staphylococcus was associated with epidermal barrier damage, including elevated levels of trans-epidermal water loss and pH, while Cutibacterium had a positive correlation with water content. Malassezia was also found to be related to an increased itching score and disease severity. Further studies focusing on the interactions between various microbes and the host and microbes can help us to better understand the pathogenesis of SD/DF.

Continuous clinical improvement of mild-to-moderate seborrheic dermatitis and rebalancing of the scalp microbiome using a selenium disulfide-based shampoo after an initial treatment with ketoconazole

OBJECTIVE

Scalp seborrheic dermatitis (SD) is a chronic, relapsing, and inflammatory scalp disease. Studies indicate a global bacterial and fungal microbiota shift of scalp SD, as compared to healthy scalp. Ketoconazole and selenium disulfide (SeS₂ ) improve clinical signs and symptoms in both scalp dandruff and SD.

AIM

The main objective of this study was to investigate the changes in the scalp microbiota diversity and counts in subjects with scalp SD during a two-phase treatment period.

MATERIAL AND METHODS

The scalp microbiota and clinical efficacy were investigated in 68 subjects with mild-to-moderate scalp SD after an initial one-month treatment with 2% ketoconazole, and after a 2-month maintenance phase, either with a 1% SeS₂ -based shampoo or its vehicle.

RESULTS

Thirty one subjects in the active and 37 subjects in the vehicle group participated. Ketoconazole provided an improvement of clinical symptoms (adherent (-1.75 p < 0.05), non-adherent (-1.5, p < 0.05)) flakes and erythema (scores 1.67-0.93, p < 0.001), in an increased fungal diversity and in a significant (p < 0.005) decrease of Malassezia spp. SeS₂ provided an additional clinical improvement (-0.8; p = 0.0002 and -0.7; p = 0.0081 for adherent and non-adherent flakes, respectively, at Day 84) compared to the vehicle associated with a low Malassezia spp. count and an additional significant (p < 0.001) decrease of the Staphylococcus spp. level.

CONCLUSION

Selenium disulfide provides an additional benefit on the scalp microbiota and in clinical symptoms of SD and dandruff after treatment with ketoconazole. The results confirm the role of Staphylococcus spp. in scalp SD and open possible perspectives for preventing relapses.

Recombinant human thymosin beta-4 (rhTβ4) improved scalp condition and microbiome homeostasis in seborrheic dermatitis

Seborrheic dermatitis (SD) is a recurrent common inflammatory skin disease that affects all ethnic groups in all regions worldwide. However, no specific treatment or preventive measure is yet available. Identifying effective treatments with acceptable safety and tolerability is desirable. In this study, scalp microbiota alterations were measured in SD, showing significantly greater abundance of Malassezia and Staphylococcus and diminished fungal and bacterial diversity compared with healthy controls. We investigated the benefit of a 4‐week treatment with 0.5 mg ml^‐1 recombinant human thymosin β4 (rhTβ4) gel or 2% ketoconazole lotion on the scalp condition of 71 patients with SD compared with 21 healthy individuals. Clinical assessment (Adherent Scalp Flaking Score, and the Maximum Erythema Area) and physiological conditions (transepidermal water loss, hydration, and sebum secretion) were evaluated. The rhTβ4 treatment provided significantly greater efficacy than ketoconazole and a sustained effect in the treatment of scalp SD. More importantly, rhTβ4 dramatically improved the microbiome homeostasis and prompted a shift of scalp microflora towards healthy composition, helping symptoms and ameliorating physiological conditions more effectively and durably than ketoconazole. Our research demonstrated the scalp microbe dysbiosis of SD and highlighted rhTβ4 as a promising therapeutic strategy in the prevention and treatment of SD.

Antimicrobial peptides and proteins: Interaction with the skin microbiota

The cutaneous microbiota comprises all living skin microorganisms. There is increasing evidence that the microbiota plays a crucial role in skin homeostasis. Accordingly, a dysbiosis of the microbiota may trigger cutaneous inflammation. The need for a balanced microbiota requires specific regulatory mechanisms that control and shape the microbiota. In this review, we highlight the present knowledge suggesting that antimicrobial peptides (AMPs) may exert a substantial influence on the microbiota by controlling their growth. This is supported by own data showing the differential influence of principal skin-derived AMPs on commensal staphylococci. Vice versa, we also illuminate how the cutaneous microbiota interacts with skin-derived AMPs by modulating AMP expression and how microbiota members protect themselves from the antimicrobial activity of AMPs. Taken together, the current picture suggests that a fine-tuned and well-balanced AMP-microbiota interplay on the skin surface may be crucial for skin health.

Skin Commensal Fungus Malassezia and Its Lipases

Malassezia is the most abundant genus in the fungal microflora found on human skin, and it is associated with various skin diseases. Among the 18 different species of Malassezia that have been identified to date, M. restricta and M. globosa are the most predominant fungal species found on human skin. Several studies have suggested a possible link between Malassezia and skin disorders. However, our knowledge on the physiology and pathogenesis of Malassezia in human body is still limited. Malassezia is unable to synthesize fatty acids; hence, it uptakes external fatty acids as a nutrient source for survival, a characteristic compensated by the secretion of lipases and degradation of sebum to produce and uptake external fatty acids. Although it has been reported that the activity of secreted lipases may contribute to pathogenesis of Malassezia, majority of the data were indirect evidences; therefore, enzymes' role in the pathogenesis of Malassezia infections is still largely unknown. This review focuses on the recent advances on Malassezia in the context of an emerging interest for lipases and summarizes the existing knowledge on Malassezia, diseases associated with the fungus, and the role of the reported lipases in its physiology and pathogenesis.

Longitudinal study of the scalp microbiome suggests coconut oil to enrich healthy scalp commensals

Dandruff is a recurrent chronic scalp disorder, affecting majority of the population worldwide. Recently a metagenomic study of the Indian scalp microbiome described an imperative role of bacterial commensals in providing essential vitamins and amino acids to the scalp. Coconut oil and its formulations are commonly applied on the scalp in several parts of the world to maintain scalp health. Thus, in this study we examined the effect of topical application of coconut oil on the scalp microbiome (bacterial and fungal) at the taxonomic and functional levels and their correlation with scalp physiological parameters. A 16-weeks-long time-course study was performed including 12-weeks of treatment and 4-weeks of relapse phase on a cohort of 140 (70 healthy and 70 dandruff) Indian women, resulting in ~ 900 metagenomic samples. After the treatment phase, an increase in the abundance of Cutibacterium acnes and Malassezia globosa in dandruff scalp was observed, which were negatively correlated to dandruff parameters. At the functional level, an enrichment of healthy scalp-related bacterial pathways, such as biotin metabolism and decrease in the fungal pathogenesis pathways was observed. The study provides novel insights on the effect of coconut oil in maintaining a healthy scalp and in modulating the scalp microbiome.

The Potential Relevance of the Microbiome to Hair Physiology and Regeneration: The Emerging Role of Metagenomics

Human skin and hair follicles are recognized sites of microbial colonization. These microbiota help regulate host immune mechanisms via an interplay between microbes and immune cells, influencing homeostasis and inflammation. Bacteria affect immune responses by controlling the local inflammatory milieu, the breakdown of which can result in chronic inflammatory disorders. Follicular microbiome shifts described in some inflammatory cutaneous diseases suggest a link between their development or perpetuation and dysbiosis. Though the hair follicle infundibulum is an area of intense immunological interactions, bulb and bulge regions represent immune-privileged niches. Immune privilege maintenance seems essential for hair growth and regeneration, as collapse and inflammation characterize inflammatory hair disorders like alopecia areata and primary cicatricial alopecia. Current research largely focuses on immunological aberrations. However, studies suggest that external stimuli and interactions across the follicular epithelium can have profound effects on the local immune system, homeostasis, and cycling. Herein, we review hair follicle bacterial colonization, its possible effects on the underlying tissue, and links to the pathogenesis of alopecia, beyond the pure investigation of specific species abundance. As skin microbiology enters the metagenomics era, multi-dimensional approaches will enable a new level of investigations on the effects of microorganisms and metabolism on host tissue.

Gut-Skin Axis: Current Knowledge of the Interrelationship between Microbial Dysbiosis and Skin Conditions

The microbiome plays an important role in a wide variety of skin disorders. Not only is the skin microbiome altered, but also surprisingly many skin diseases are accompanied by an altered gut microbiome. The microbiome is a key regulator for the immune system, as it aims to maintain homeostasis by communicating with tissues and organs in a bidirectional manner. Hence, dysbiosis in the skin and/or gut microbiome is associated with an altered immune response, promoting the development of skin diseases, such as atopic dermatitis, psoriasis, acne vulgaris, dandruff, and even skin cancer. Here, we focus on the associations between the microbiome, diet, metabolites, and immune responses in skin pathologies. This review describes an exhaustive list of common skin conditions with associated dysbiosis in the skin microbiome as well as the current body of evidence on gut microbiome dysbiosis, dietary links, and their interplay with skin conditions. An enhanced understanding of the local skin and gut microbiome including the underlying mechanisms is necessary to shed light on the microbial involvement in human skin diseases and to develop new therapeutic approaches.