What Is the Skin Microbiome?
Human skin is not a sterile surface — it is a dynamic ecosystem inhabited by billions of microorganisms. On average, 1 million bacteria are found per cm² of skin surface; fungi, viruses, and mites are also part of the microbiome. This community is referred to as the "skin flora" or "skin microbiome."
Data from the Human Microbiome Project have revealed more than 1,000 distinct bacterial species on the skin surface. However, dominant species differ by anatomical region: in sebaceous areas (forehead, sides of the nose), Cutibacterium acnes (formerly Propionibacterium acnes) predominates, while Staphylococcus epidermidis and Corynebacterium species are more prominent in dry areas (arms, legs).
Composition of the Skin Microbiome: Key Players
| Microorganism | Location | Normal Function | Role in Dysbiosis |
|---|---|---|---|
| Cutibacterium acnes | Sebaceous areas (face, chest, back) | Sebum breakdown, fatty acid production, pH maintenance | Type IA strain → inflammatory acne |
| Staphylococcus epidermidis | Entire body surface | Produces antimicrobial peptides against S. aureus; supports the skin barrier | When reduced: S. aureus colonisation → atopic dermatitis |
| Staphylococcus aureus | Minimal in healthy skin | Remains in the background on healthy skin | Increases with dysbiosis → triggers eczema, impetigo |
| Malassezia | Scalp, face (especially glabella) | Lipid metabolism | Overgrowth → seborrhoeic dermatitis, pityriasis versicolor |
| Corynebacterium spp. | Dry areas | Urea hydrolysis, pH regulation | Erythema and odour changes |
What Is Dysbiosis and How Does It Develop?
Dysbiosis is the disruption of the healthy balance of the skin microbiome. The overgrowth of certain species or the decline of beneficial species undermines microbiome integrity and creates a foundation for skin disease. The main causes of dysbiosis include:
- Over-cleansing: Frequent use of high-pH soaps and foaming cleansers disrupts the acid mantle and prevents beneficial species from adhering to the skin
- Broad-spectrum antibiotics: Systemic antibiotics affect both the gut and skin microbiome; topical antibiotics (clindamycin) lead to C. acnes resistance with prolonged use
- Environmental pollution: Air pollutants (PM2.5, ozone, heavy metals) directly affect the skin microbiome; microbiome diversity is noticeably lower in urban dwellers compared with those in rural areas
- Alcohol-based toners and antiseptic products: Non-specific antimicrobial action affects both harmful and beneficial species
- Stress: Elevated cortisol increases inflammatory cytokine release and adversely affects the skin microbiome
The Acne–Microbiome Connection: Are All C. acnes Strains Equal?
For many years, a direct causal relationship between P. acnes (now C. acnes) and acne was assumed. However, a landmark 2016 study fundamentally changed this view: different strains of C. acnes play very different roles in acne pathogenesis.
C. acnes Type IA is markedly dominant in acne lesions and triggers the production of inflammatory cytokines. By contrast, Type IB and Type II strains are common on healthy skin and are not associated with acne. These findings explain why a "total eradication of C. acnes" strategy has achieved limited success — and why preserving microbiome balance is a more sustainable approach.
Eczema (Atopic Dermatitis) and the Microbiome
In individuals with atopic dermatitis, the proportion of S. epidermidis decreases markedly while S. aureus increases — sometimes reaching up to 90%. S. aureus produces proteases and toxins that impair barrier function, trigger inflammatory reactions, and intensify itching.
For this reason, treatment of atopic dermatitis must not only suppress inflammation (corticosteroids) but also re-establish microbiome balance. Promising clinical studies on S. epidermidis-enriched probiotic skin preparations are ongoing.
Rosacea and the Microbiome
In individuals with rosacea, the density of Demodex folliculorum on facial skin is markedly elevated (6–18 times higher than in healthy individuals). A reduction in S. epidermidis and a specific increase in Bacillus oleivorans have also been identified in these patients. In rosacea, microbiome imbalance goes hand in hand with skin barrier dysfunction, and treatment must target both simultaneously.
Probiotic Skincare: The Difference Between Prebiotics, Probiotics, and Postbiotics
| Category | Definition | Skincare Example | Mechanism of Action |
|---|---|---|---|
| Prebiotic | Nutrients that support the growth of beneficial bacteria | Inulin, beta-glucan, fructooligosaccharides | Selective stimulation of S. epidermidis and beneficial species |
| Probiotic | Live beneficial microorganisms | Serums containing Lactobacillus or Bifidobacterium lysate | Competitive inhibition, antimicrobial peptide production |
| Postbiotic | Bacterial metabolites and cell wall components | Fermented extracts, bacterial lysates, short-chain fatty acids | Barrier support, anti-inflammatory signalling |
The vast majority of "probiotic" claims in cosmetic products are in fact postbiotic in nature; maintaining the shelf stability of formulas containing live bacteria is extremely challenging. Postbiotics (fermented extracts, lysates) are clinically effective and offer far greater stability.
A Guide to Protecting and Supporting the Skin Microbiome
Core principles for building a microbiome-friendly skincare routine:
- Choose a pH-balanced cleanser: Cleansers formulated within a pH of 4.5–5.5 preserve the acid mantle and skin flora
- Avoid over-cleansing: A gentle rinse or minimal cleanser in the morning and double cleansing in the evening — anything more suppresses the microbiome
- Avoid prolonged topical antibiotics: Clindamycin and erythromycin monotherapy should not exceed 3 months; combining with benzoyl peroxide reduces resistance development
- Incorporate prebiotic ingredients: Moisturisers containing inulin, beta-glucan, or oat extract support the microbiome
- Prioritise barrier repair: A compromised barrier predisposes to dysbiosis; products containing ceramides and niacinamide protect both the barrier and the microbiome
- Pay attention to diet: The gut microbiome and skin microbiome are strongly interconnected (gut–skin axis); fermented foods, prebiotic fibres, and a low-sugar diet positively influence skin flora
The Relationship Between Barrier Repair and the Microbiome
The skin barrier and the microbiome function as two mutually supportive systems. A robust barrier prevents pathogenic species from colonising and allows beneficial species to thrive in an acidic environment. In turn, beneficial species such as S. epidermidis contribute to barrier function by stimulating β-defensin production.
Barrier damage leads to dysbiosis, and dysbiosis leads to deeper barrier damage — this vicious cycle is the most critical mechanism underlying atopic dermatitis, rosacea, and chronic acne. Treatment of these conditions must therefore target both barrier repair and microbiome balance simultaneously.
Microbiome-Focused Approach at Virtuana Clinic
At Virtuana Clinic, a microbiome perspective is incorporated into the standard assessment protocol for presentations of chronic acne, atopic dermatitis, and rosacea. The duration and discontinuation of topical antibiotic therapy, benzoyl peroxide combination strategies, and simultaneous planning of barrier repair routines are the core elements of this approach.
Prebiotic-containing cosmetics are recommended as a complement to medical treatment, and up-to-date literature on oral probiotic support is shared with patients. A microbiome restoration protocol is applied especially following prolonged antibiotic therapy.
This article is for informational purposes only. Please consult a qualified physician for treatment decisions.