Skin microbiome and inflammatory dermatoses: A focused review

INTRODUCTION

The skin serves as both a physical barrier and a dynamic environment for a variety of microorganisms, such as bacteria, fungi, viruses, and mites. They create the skin microbiome, which is essential for maintaining skin homeostasis by regulating immune responses, promoting barrier function, and defending against pathogenic invasion. Important commensals such as Staphylococcus epidermidis and Cutibacterium acnes are required for immune regulation and microbial homeostasis.^[1]

Disruption of this balance, known as dysbiosis, can cause or exacerbate inflammatory skin conditions. Atopic dermatitis (AD), psoriasis, acne, rosacea, seborrheic dermatitis, and hidradenitis suppurativa have all shown different variations in microbial composition and diversity. Overcolonization of Staphylococcus aureus and decreased microbial diversity, for example, are associated with Alzheimer’s disease severity, whereas changes in Malassezia and Demodex populations are associated with seborrheic dermatitis and rosacea, respectively.^[2,3]

Recent research has shown how microbial metabolites and strain-level variations influence inflammatory pathways such as toll-like receptor signaling and T-helper cell type 1/T-helper cell type 17 (Th17) activation. These findings highlight the microbiome’s importance not only in disease causation but also as a possible treatment target. This study investigates the complex link between the skin microbiota and inflammatory dermatoses, focusing on potential diagnostic and therapeutic options through microbiome manipulation.^[4,5]

This review is unusual in that it brings together recent breakthroughs in skin microbiome research, focusing on disease-specific dysbiosis patterns and new microbiome-targeted therapeutics. It provides a complete view for future clinical and translational dermatology research by combining insights from molecular pathways, diagnostic breakthroughs, and individualized treatment options.

HEALTHY SKIN MICROBIOME

Maintenance of the cutaneous barrier is critical for preventing pathogenic infection, which is why traditional skin microbiology has long focused on the prevention and treatment of infections by well-known pathobionts. The skin is second only to the gut in bacterial density, with approximately 10⁴–10⁶ bacteria per square centimeter and over 200 genera identified, as illustrated in Figure 1.^[6,7] It is home to 18 bacterial phyla, with four dominant ones accounting for 99% of the microbial population: Actinobacteria (51.8%), Firmicutes (24.4%), Proteobacteria (16.5%), and Bacteroidetes (6.3%).^[6]

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Figure 1:

Healthy skin microbiome.

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Although skin microbiome research remains less developed than that of the gut, it has already revealed important roles in maintaining homeostasis. The skin acts as a first-line defense against microbial invasion through tight junctions between corneocytes in the stratum corneum (forming a physical barrier) and through antimicrobial peptides and lipids secreted by keratinocytes and glands (forming a chemical barrier).^[8] The skin microbiota contributes by synthesizing nutrients (e.g., vitamins and amino acids), inhibiting pathogenic growth, priming the immune system to distinguish between commensals and pathogens, and regulating epidermal differentiation.^[9-12]

Most of the skin microbiome comprises stable resident microbes, though transient microbes can opportunistically colonize compromised skin. Similar to the gut, skin microbial communities are spatially distinct and shaped by cutaneous topography. While site-specific compositions are largely conserved, they can be influenced by factors such as age, ethnicity, genetics, climate, and skincare habits.^[13,14] Furthermore, many skin diseases present in a site-specific manner and are associated with altered microbiomes, highlighting the value of investigating microbial occupancy of ecological niches for understanding skin pathologies.^[15]

Skin microbiota is specialized to exploit the chemical environment of the stratum corneum, sweat, and sebaceous glands. Microbial composition varies by region, reflecting differences in ultraviolet exposure, temperature, moisture, sebum content, oxygen levels, and pH. Sebaceous (oily) sites such as the face, back, and torso are highly acidic due to abundant free fatty acids and are predominantly inhabited by sebum-metabolizing bacteria such as C. acnes (formerly Propionibacterium). Staphylococcus is the second most predominant genus in these areas, with species such as S. aureus and S. epidermidis producing lipases and tolerating the acidic environment.^[16]

Corynebacteria are dominant colonizers of warm and moist environments, while halotolerant Staphylococci thrive in salt-rich sites like sweat glands. Dry sites (e.g., hypothenar palm, volar forearm) exhibit high microbial diversity and low temporal stability. The foot mycobiome is also uniquely diverse, including Malassezia, Aspergillus, Cryptococcus, Rhodotorula, and Epicoccum.^[17,18]

Sebaceous regions (e.g., facial skin, upper chest, and back) are less diversified than moist (nares, axillae, antecubital, and popliteal fossae) and dry regions (e.g., volar forearm ). C. acnes is the most prevalent species in both sebaceous and dry areas; however, no one bacterial species dominates moist areas, though Corynebacterium and Staphylococcus spp. are relatively most abundant.^[19,20] Figure 1 shows an illustrative understanding of the healthy skin microbiome.

SKIN MICROBIOME DYSBIOSIS IN INFLAMMATORY SKIN DISORDERS

Skin microbiome dysbiosis is a key factor in inflammatory skin illnesses such as psoriasis, AD, and acne vulgaris. Changes in microbial communities affect skin homeostasis, resulting in immunological responses and inflammation. Table 1 shows skin microbiome dysbiosis in common inflammatory dermatoses.

MICROBIOME-BASED DIAGNOSTIC AND THERAPEUTIC APPROACHES

Patients with AD are more susceptible to acquiring bacterial skin infections, which can cause serious morbidity and spread throughout the body if not treated promptly. Weeping sores, honey-colored crusts, and pustules are frequent symptoms of bacterial infection. However, the clinical presentation of bacterial infection in AD varies widely, and the primary symptoms of AD – cutaneous erythema and warmth, seeping associated with edema, and regional lymphadenopathy – overlap with those of infection, making clinical diagnosis challenging. Furthermore, some indications may be obscured by anatomical site and skin-type characteristics. Furthermore, the high frequency of S. aureus colonization in AD renders positive skin swab cultures of suspected infection worthless as a diagnostic tool.^[47]

Shotgun metagenomics provides various advantages for studying microbial communities, particularly those found on human skin. One of its main advantages is comprehensive DNA profiling, which collects the entire genetic material from all species in a sample, providing a more accurate and impartial assessment of microbial diversity than specialized amplicon-based approaches. This approach also improves taxonomic resolution, allowing for fine-scale distinction of closely related microbial species and strains, such as the many Staphylococcus species present on human skin. Furthermore, shotgun metagenomics extends beyond identifying microorganisms; it allows for functional analysis by discovering genes related to metabolic pathways and virulence factors, revealing the skin microbiome’s functional potential.^[47,62]

Short-read platforms such as illumina continue to be popular in sequencing due to their excellent accuracy and throughput. However, long-read sequencing platforms such as Oxford Nanopore and PacBio are gaining popularity due to their capacity to cover complicated and repetitive genomic areas, allowing for better genome assembly and structural variation detection.^[62] For data analysis, two basic methodologies are used. Reference-based approaches involve matching sequencing data to known microbial genomes, which enables the identification and quantification of known taxa.^[63,64] In contrast, assembly-based techniques try to recreate genomes directly from sequencing data. This results in the development of metagenome-assembled genomes, which can reveal new and previously unknown bacteria. Together, these advances make shotgun metagenomics a potent tool for investigating the composition and functional dynamics of the skin microbiome.^[65]

Acne vulgaris is a common dermatological illness characterized by the appearance of a variety of lesions, including whiteheads, blackheads, pustules, papules, and cysts. Its cause is multifaceted, including aberrant keratinization of the sebaceous canal, bacterial colonization (especially by C. acnes), increased sebum production, hormonal imbalances, and hereditary predispositions. Recent studies have underlined the importance of the gut-skin axis, in which the intestinal microbiota plays a critical role in immune regulation and systemic inflammation. Dysbiosis, or an imbalance in the gut microbiota, can aggravate acne by triggering inflammatory responses on the skin. In light of these findings, probiotics have emerged as a possible therapeutic option for acne management.^[66] Both oral and topical probiotic preparations have been demonstrated to restore microbial balance, reduce inflammation, improve skin barrier function, and limit the growth of pathogenic bacteria such as C. acnes. Reflecting this scientific interest, the global markets for probiotic supplements and microbiome-friendly cosmetics are quickly rising, indicating an increasing need for microbiome-targeted approaches to skin health and acne treatment.

The skin microbiome, which includes a wide variety of microorganisms, is critical to maintaining skin health and equilibrium. Disruptions in this microbial balance are connected with numerous skin problems, such as AD, acne, and psoriasis.^[67] Prebiotics, non-digestible food components that benefit the host by selectively encouraging the growth and/or activity of beneficial microbes, have received interest due to their potential for skin health. Prebiotics applied topically have been demonstrated to modify the skin microbiome, boosting helpful bacterium growth while inhibiting pathogenic species. This modulation can lead to increased skin barrier function, decreased inflammation, and enhanced overall skin look.^[68]

In dermatology, the use of prebiotics in skincare formulations attempts to restore and maintain a healthy skin microbiome. Prebiotics can help regulate microbially imbalanced skin problems by creating a beneficial microbial environment. For example, in AD, where S. aureus is frequently dominant, prebiotic therapies can help re-establish microbial diversity and lower disease severity.^[68,69]

Furthermore, the beneficial combination of probiotics and prebiotics, also known as synbiotics, is being investigated to improve therapeutic effects in skin health. Probiotics deliver beneficial living bacteria, whereas prebiotics nourish these germs, promoting their growth and activity. This combined strategy shows promise in strengthening the skin’s natural defenses and alleviating a variety of dermatological disorders.^[70]

As we learn more about the function of the skin microbiome in acne etiology, treatment efforts are shifting toward targeted microbiome modulation. Acne is tightly linked to dysbiosis inside the pilosebaceous unit, particularly with C. acnes strains that cause inflammation and immunological response. Traditional therapies include topical antibiotics and benzoyl peroxide, while beneficial, frequently alter microbial diversity and contribute to antimicrobial resistance. In response, novel therapeutic techniques have arisen that attempt to restore microbial equilibrium while avoiding broad-spectrum antibiotic effects. Topical microbiome modulators, such as probiotics, postbiotics, and drugs that modulate microbial signaling pathways, provide interesting alternatives.^[58] These treatments may improve skin barrier function, lower pathogenic bacterial pathogenicity, and promote the proliferation of commensal flora. Modulating host targets, such as peroxisome proliferator-activated receptor gamma, can reduce sebaceous gland activity and inflammation while maintaining microbial balance. Collectively, these discoveries point to a future in acne treatment in which therapeutic efficacy is accomplished by ecological balance rather than microbial eradication.^[71] Table 2 shows a detailed understanding of these therapeutic approaches.

CHALLENGES AND KNOWLEDGE GAPS

The application of artificial neural networks to represent gut microbiota-derived chemicals has interesting implications for predicting their impact on skin problems. However, simulation-based predictions must be confirmed using in vitro and in vivo experiments.^[72] Certain microbes, such as Bifidobacterium and Fusicatenibacter, can protect against acne by modulating IL-10 and regulating the lipopolysaccharide (LPS) barrier. However, Bacteroides and the Ruminococcus torques group are linked to increased inflammatory markers such as IL-6, TNF-α, and IL-1β in acne and rosacea.^[73-75]

Short-chain fatty acids, notably those from Bacteroidetes, have anti-inflammatory properties in psoriasis through increasing regulatory T cells and decreasing IL-17. However, inconsistent results on microbial abundance, variety, and directionality in psoriasis impede clinical translation. Furthermore, taxa mimic psoriasis by activating regulatory T cells and inhibiting IL-17.^[76] However, there is mixed evidence that microbial abundance promotes regulatory T cells while decreasing IL-17. However, Ruminococcaceae play both protective and harmful functions in several dermatoses, which can lead to confusion in interpretation.^[26,77]

Technological limits also exist. Although sensitive, next-generation sequencing runs the danger of cross-contamination, particularly in low-biomass samples, emphasizing the importance of robust controls. Methodological differences, such as relying on fecal rather than mucosal samples and using different sequencing targets, further decrease comparability.^[78-80]

Small sample sizes, unstandardized diets, and a lack of multicenter collaboration all contribute to further biases. Environmental, genetic, and ethnic variables (for example, sebum secretion among cultures) all influence microbiome variability. For example, in AD, the lesional microbiota varies significantly between and among patients, with S. aureus abundance associated with microbial instability.^[81-83] Furthermore, dietary and regional factors, which are infrequently reported in contemporary studies, have a significant impact on the gut-skin axis. To better understand causative linkages and enhance microbiome-targeted therapeutics for inflammatory dermatoses, future research should include nutritional assessments, use various sampling methodologies, and account for longitudinal variability.^[84-86]

THE FUTURE OF PERSONALIZED SKIN MICROBIOME THERAPIES IN DERMATOLOGY

Recent discoveries in skin microbiome research are revolutionizing our understanding of dermatologic illness and treatment. The skin is home to a varied range of microbial populations that produce antimicrobial peptides, enzymes, and signaling molecules that can influence local skin health or disrupt the microbial balance. With growing evidence of these interactions, scientists are investigating the use of live microbial agents to prevent or cure inflammatory skin illnesses such as AD, acne, and hidradenitis suppurativa.^[87]

Several early-stage clinical trials are underway to assess topical applications of beneficial bacteria, such as Staphylococcus hominis, which have been modified to express antimicrobial chemicals. These experimental treatments seek to restore the skin microbiome and alleviate illness flares. Unlike over-the-counter “probiotic” skincare creams, these therapies are thoroughly clinically tested. Dosing frequency, formulation type, and administration site are all important factors in determining long-term efficacy.^[88,89]

Parallel to this medicinal progress, technological advancements, particularly in AI and bioinformatics, are changing the way we interpret microbiome data. As sequencing technology advances, machine learning algorithms are increasingly being utilized to map microbial profiles, forecast disease risk, and drive personalized treatment plans. These computational approaches can discover microbial fingerprints associated with disease progression or response to medication, allowing for a more tailored approach to skin health. Furthermore, incorporating microbiome health into normal dermatologic therapy may significantly improve chronic disease management. By conserving good microorganisms and limiting unnecessary antibiotic use, doctors can lower the chance of resistance while promoting long-term skin stability. Therapies that promote microbiome resilience, such as bacteriophage treatments targeting C. acnes or the use of postbiotics, are demonstrating early promise in terms of inflammation reduction and skin barrier improvement [Figure 2].^[89,90]

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Figure 2:

Schematic flowchart of skin dysbiosis leading to inflammatory dermatoses.

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CONCLUSION

The complex association between the skin microbiota and inflammatory dermatoses demonstrates the microbiome’s critical involvement in skin health and illness. As research improves, it becomes clear that dysbiosis plays a key role in the development of disorders such as AD, psoriasis, and acne vulgaris. Novel discoveries of microbial metabolites, immunological signaling pathways, and microbial strain-specific behavior have paved the road for microbiome-targeted diagnostics and treatments. Emerging treatments, such as engineered commensals, topical probiotics, and phage therapy, provide intriguing alternatives to standard antimicrobials by restoring microbial balance while preserving beneficial flora. Furthermore, technical advancements in metagenomics and machine intelligence enable exact microbial characterization and tailored intervention techniques. Despite these developments, some obstacles remain, including inconsistencies in clinical data, technical constraints, and unpredictability caused by environmental and individual factors. To close these gaps, future research should focus on standardized methodology, longitudinal investigations, and the integration of host-microbiome-environmental interactions. Overall, a better understanding of the skin microbiome’s function in dermatological illnesses ushers in a new era of precision dermatology. Personalized microbial modulation solutions have the potential to improve chronic skin disease care by shifting the focus away from broad-spectrum treatments and toward individualized, microbiome-preserving approaches that ensure efficacy and sustainability.