SKIN MICROBIOME 35


bacteria (Staphylococcus aureus, streptococci) and Gram (-) bacteria (e.g. Enterobacteriaceae from the intestinal flora). It has been found that female skin microbiota


tends to be more diverse due to many factors such as pH, hormones, hygiene, sweating, and vaginal flora.12


The resident flora is in permanent competition


with the transient flora. Its “land occupation” strategies are: ■ A significant coverage of the epidermis (> 1000 species and 1010


to 1014 bacteria / cm2 )


■ High adhesion to the surface of keratinocytes (biofilms) ■ Competitive use of available nutrients ■ The production of antimicrobial cationic peptides by bacteria (Bacteriocins) as well as by keratinocytes (Defensins in particular)


Influence of cosmetic products on the composition of the skin microbiome The composition of the skin microbiome is shaped by a complex interplay of intrinsic host characteristics and external environmental exposures. Physiological determinants such as genetics, immune activity, skin pH, lipid composition and hydration create selective niches that favour specific microbial communities. These internal factors interact continuously


with extrinsic influences, including climate, pollution, hygiene habits, cosmetic product use, diet, lifestyle and circadian rhythms—which modulate microbial diversity and stability over time. Understanding how these factors interact is essential for predicting how the skin ecosystem responds to stressors, skincare interventions or pathological conditions.


Cosmetic Products: interaction with the skin microbiome The effect of cosmetics on the skin microbiome is neither inherently positive nor negative. It depends on how the formulation maintains the ecological equilibrium between microbial residents and the skin’s biophysical state. Formulations designed with pH balance, barrier


reinforcement, and selective antimicrobial control can actively promote a resilient, well-adapted microbiome, supporting claims of ‘microbiome balance’, ‘skin harmony’, and ‘microbiota-friendly’ skin care. Cosmetic products constantly interact with


the skin’s physicochemical environment and thus have a measurable impact on the composition, diversity, and metabolic activity of the resident microbiota. This influence can be either supportive, when the formulation maintains homeostasis and promotes resilience, or disruptive when it alters key parameters such as pH, hydration, sebum composition, and nutrient availability.13


Cleansers and surfactant systems Cleansers exert one of the most direct and repeated influences on the skin microbiome. While they are deemed essential for hygiene and the removal of sweat, oil, and debris, surfactant systems can transiently strip lipids and increase


www.personalcaremagazine.com Stomach Composition


largely dependent on body part


Intestine Mouth Skin Nose Lung


Viruses


Bacteriophages Eukaryotic viruses


Cladrosporium Candida Aspergillus


Malassezia Others Saccharomyces


Bacteria


Cyanobacteria Bacteroidetes Actinobacteria


Firmicutes Fusobacteria Proteobacteria


Vagina


Figure 1: The integrated microbiome of human body10


transepidermal water loss (TEWL) consequently shifting the skin microenvironment toward dryness and elevated pH. This transient disruption often favours


Staphylococcus and Corynebacterium dominance while reducing Cutibacterium acnes populations, as these bacteria differ in tolerance to hydration and oxygen levels.14 Formulating technologies aimed to preserve


lipid film continuity and maintain acidic skin pH (~5) are beneficial for supporting microbial stability and recovery within hours after washing.15 Emollients, occlusives, and barrier lipids The lipid phase of a cosmetic product—whether natural oils, esters, or silicones—plays a pivotal role in shaping microbial ecology. Lipids provide substrates and energy sources for specific bacteria (notably Cutibacterium acnes), and the relative proportion of saturated vs. unsaturated fatty acids influences microbial growth patterns. Occlusive agents (petrolatum, dimethicone,


waxes) can transiently lower oxygen availability, selectively favouring anaerobic or microaerophilic taxa, while non-occlusive emollients (triglycerides, squalane, esters) better maintain aerobic- anaerobic balance. In addition, ceramide-rich formulations


improve barrier integrity, lowering TEWL and stabilizing the commensal community structure.16


Actives, prebiotics and postbiotics Modern skin care formulations are evolving from ‘non-disruptive’ to microbiome-supportive design. Prebiotics such as inulin, α-gluco- oligosaccharides and xylitol, or Lactobacillus ferment filtrates provide selective nutrients that reinforce beneficial strains like S. epidermidis, while postbiotics (lysates, bacteriocins, enzymes) can directly modulate host immunity and suppress opportunistic pathogens without broad antibacterial effects.17


Emerging evidence


indicates that certain actives such as niacinamide, panthenol, and ceramide precursors, not only enhance barrier function but also indirectly stabilize microbial diversity by reducing inflammatory and oxidative stress conditions unfavourable to commensals. Postbiotics, including Lactobacillus ferment lysate and Bifida ferment filtrate, deliver peptides and metabolites that regulate antimicrobial peptide expression and Toll Like Receptors (TLR) -mediated immune tolerance.17, 18


Clinical trials with Lactobacillus


ferment- based cosmetics have reported a 25–30% increase in microbial evenness, 20%


March 2026 PERSONAL CARE MAGAZINE


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