Understanding the Microbiome: Implications for Skin Health and Practice

By Maria Rylott-Byrd

The Microbiome, a balanced ecosystem. Artist impression by Elena Mozhvilo

Understanding the microbiome is now essential for anyone working in skin health. It influences how the skin defends itself, how it responds to inflammation and how predictably it heals. For therapists, this knowledge moves treatment planning beyond topicals and protocols and into a deeper understanding of the systems that maintain skin homeostasis.

Microbial colonisation begins at birth, with vaginal delivery exposing the infant to maternal vaginal and intestinal microbes, followed by further diversification through breastfeeding. Caesarean delivery results in a different microbial starting point, yet these early distinctions still shape the maturation of the immune system and the development of epithelial tissues across both the gut and the skin, creating long-term patterns of tolerance, inflammation and microbial resilience.

Although structurally different, the skin and gut share several fundamental characteristics. Both are epithelial barriers in constant contact with the external environment. Both rely on vascular, neural, endocrine and immune inputs. Both depend on regulated stem-cell turnover. Each maintains a long-term relationship with its resident microbiota and each uses microbial signals to determine whether to mount a defence or maintain tolerance. A disturbance in one system often triggers measurable effects in the other, forming what is now widely recognised as the bi-directional gut–skin axis.

When the gut becomes imbalanced, the consequences are widespread. Dysbiosis reduces short-chain fatty acids, particularly butyrate, which is essential for regulating inflammation, maintaining mucosal integrity and supporting the renewal of intestinal epithelial cells. Without adequate butyrate, tight-junction proteins weaken, allowing intestinal contents to pass into circulation. This increase in permeability, commonly referred to as leaky gut, creates an inflammatory burden that can amplify cutaneous issues such as sensitivity, impaired barrier function and chronic inflammatory skin conditions. Vitamin D synthesis through UVB exposure also has a regulatory effect on the gut microbiome, influencing systemic immune responses that extend to the skin.

The skin hosts an equally complex ecosystem, with an estimated 10,000 to 100,000 microorganisms per square centimetre. This community includes bacteria, fungi, viruses and mites, all living on a surface governed by the acid mantle, a hydrolipidic film with a pH between 4.5 and 5.5. This slightly acidic environment is essential for microbial balance and for the enzymes responsible for corneocyte maturation, lipid processing and barrier cohesion. When the acid mantle shifts, microbial populations shift with it.

Across the skin, four main bacterial phyla dominate. Actinobacteria such as Cutibacterium and Corynebacterium help regulate pH and support immune balance, particularly in sebaceous areas. Firmicutes, which include Staphylococcus and Streptococcus, dominate moist regions. S. epidermidis provides antimicrobial protection, while overgrowth of S. aureus is strongly associated with atopic dermatitis. Proteobacteria, including Pseudomonas and Acinetobacter, are more common on dry sites and contribute to lipid metabolism, pathogen resistance and overall microbial diversity. Bacteroidetes are less dominant but still influence microbial variety, particularly on exposed skin and may contribute to inflammation when the barrier is disrupted.

Other microorganisms also have clinical relevance. Demodex mites can contribute to certain presentations of rosacea when populations increase. Malassezia yeasts play a role in Pityrosporum Folliculitis. Viruses, including HPV and molluscum contagiosum form part of the broader virome and influence immune signalling. Each of these organisms interacts directly with the skin’s physical, chemical and immune barriers through pattern-recognition receptors such as toll-like receptors, priming the skin’s immune responses and shaping its tolerance to external and internal triggers.

Both the gut and skin microbiomes are heavily influenced by modern pressures. Gut populations shift with stress, processed foods, sugar, disrupted sleep and antibiotic use. On the skin, microbiota are affected by preservatives, pollution, high-pH cleansing, over-exfoliation or frequent exposure to strong actives. Day-to-day factors such as fabric friction, hygiene practices and medication add another layer of complexity. Because microbiomes vary by age, anatomical site, environment and genetics, their needs are never identical between clients, which makes a one-size-fits-all approach ineffective.

Microbiome-focused skincare has existed for over a century, yet formulating with live organisms remains difficult due to stability and preservation requirements. As a result, many modern formulations use alternatives. Prebiotics such as squalene and lecithin support beneficial bacteria. Ferments and lysates offer non-viable bacterial components that still influence cellular communication. Postbiotics, which are the metabolites produced by microorganisms provide anti-inflammatory, antimicrobial, antioxidant and immune-modulating benefits and are typically more stable and reliable than live probiotics.

The science highlights that the microbiome is a fundamental component of epithelial health. When therapists understand how microbial communities influence barrier integrity, inflammation, immune readiness and systemic interactions, treatment planning becomes more rational and more predictable. Supporting microbial balance, both gut and skin, strengthens the foundations of functional skin health and enhances the skin’s resilience long-term.

Maria Rylott-Byrd aka The Corneotherapy Consultant™ is the creator of Epidermal Skin Health – A Corneotherapist’s Essential Guide, a comprehensive skin science-led course designed to deepen understanding and elevate professional expertise.