34 SKIN MICROBIOME


The skin microbiome and the power of certified cosmetics


Aditee Chandak, Pierre Grascha, Mélissa Mendy – Cosmebio


The human skin hosts one of the most diverse microbiomes in the body, comprising bacteria, fungi, viruses, and archaea.1


CFU/cm2


Across more than 20


anatomical sites, bacterial density ranges from 102 to 106


, with Actinobacteria, Firmicutes,


Proteobacteria, and Bacteroidetes as the dominant phyla.2


Fungal communities are largely composed


of Malassezia spp., while viral sequences mostly correspond to bacteriophages targeting Staphylococcus and Cutibacterium species.3 Distinct ecological niches—sebaceous, moist,


and dry—offer specific nutrients, humidity, and oxygen levels that shape microbial composition.4 Sebaceous zones are dominated by Cutibacterium acnes (50–80%), moist sites by Corynebacterium and Staphylococcus spp. (40–60%), and dry areas show greater Proteobacterial diversity. Despite inter-individual variability, a core set of species (Cutibaterium acnes, Staphylococcus epidermidis, Corynebacterium kroppenstedtii) is consistently present in more than 80% of individuals.5 Commensals contribute to skin homeostasis


PERSONAL CARE MAGAZINE March 2026


through short-chain fatty acids, lipases, and antimicrobial peptides (AMPs), regulating pH and immune tolerance.6


For example, Staphylococcus


epidermidis produces phenol-soluble modulins that suppress pathogens and induce AMP expression.7 Loss of these functions correlates with


increased transepidermal water loss (TEWL) and clinical dryness.8 In conditions like atopic dermatitis or after


harsh product use, microbial alpha-diversity can drop 30–50%, with Staphylococcus aureus overgrowth. Targeted moisturizer applications can restore diversity (+15–20% Shannon index) and reduce pathogen colonization, highlighting the microbiome’s key role in maintaining skin homeostasis.8 Finally, perturbations (surfactants, antiseptics,


UV exposure) reduce alpha-diversity temporarily, but commensal populations re-establish within 24–72 hours in most individuals.9


Moisturizers


with prebiotic lipids shorten this recovery time to nearly 24 hours versus 48 hours. The integrated human microbiome extends


beyond the skin to digestive, respiratory, urinary, and reproductive systems, where disruptions similarly affect health. The concept of a ‘metaorganism” emphasizes the dynamic interactions between host and microbiota, modulated by physiological and environmental factors.


The skin microbiota The skin microbiota colonizes both the surface and inner layers of the stratum corneum, residing in skin lipids and Natural Moisturization Factor (NMF), whose acidic pH supports antimicrobial peptide production and inhibits pathogens. Its composition varies across different skin


sites. Globally, more than 90% of skin bacteria belong to four phyla: Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes, with key species including Staphylococcus epidermidis, Propionibacterium acnes, Corynebacterium, Micrococcus, Streptococcus, and Acinetobacter.12 On the other hand, the transient flora, acquired


from contact with people, animals, plants, or surfaces, is more varied and includes Gram (+)


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