SKIN MICROBIOME


The skin microbiome and mature skin


Stéphanie Badel-Berchoux, Marie Chavignon, Margaux Jeanmougin and Emma Trapeaux – Byome Labs


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The skin changes throughout life. This involves an increase in surface pH, a reduction in sebum secretion, lipid and tissue remodelling, and changes in the microbial ecosystem. The skin microbiome especially influences hydration, barrier function and inflammation. This bidirectional skin–microbiome relationship compels a re-evaluation of how products for mature skin are assessed: beyond surface observation, the objective measurement of a formula’s impact on the composition and function of the microbiome is required. Byome Labs places microbiome science


at the core of its methods. We conduct customized in vitro assays to help cosmetic, dermocosmetic, and pharmaceutical brands quantify the effects of their finished products or ingredients on the skin, scalp, oral, and vaginal microbiomes, in contexts of dysbiosis or maintenance of microbial balance. This article focuses on mature skin and on the bidirectional relationship between skin ageing and the microbiome, with implications for microbiome compatible care.


Skin ageing: factors, causes, consequences Factors: intrinsic versus extrinsic Skin ageing results from a combination of


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intrinsic factors, such as hormonal regulation and genetics, and extrinsic factors, including UV exposure, pollution, and smoking.1,2 Within this framework, a distinction is


commonly made between intrinsic ageing, which reflects the ‘programmed’ evolution of tissue functions, and extrinsic ageing, for example photoageing resulting from chronic solar exposure.2,3


maintain controlled permeability.2 In parallel, ageing is associated with a pro-


inflammatory state that disrupts cutaneous homeostasis: protection against external stressors declines, water retention deteriorates, and the overall integrity of the tissue becomes harder to preserve.2


Indeed, photoageing acts as an


accelerator of age-related alterations by modifying cutaneous lipid structure and sustaining low- grade chronic inflammation over time.1


Key mechanisms: barrier, lipids, and inflammation With age, the skin undergoes profound functional changes: decreased activity of the sebaceous and sweat glands, reduced nutrient delivery to tissues, and alkalinization of surface pH, all factors that weaken barrier function.2,4 At the level of the stratum corneum, ageing


is accompanied by structural alterations and a decline in epidermal lipids, which reduces water-retention capacity and increases vulnerability to external insults.2 More specifically, there is a significant


reduction in the three major lipid components of the barrier : ceramides, cholesterol, and free fatty acids - the balance of which is essential to


Consequences At the histological level, ageing is accompanied by epidermal atrophy, a decrease in fibroblast and collagen density, and alterations of the stratum corneum with reduced water holding capacity.1 Clinically, these rearrangements translate


into thinner, drier, and more vulnerable skin, with slower wound healing and increased susceptibility to certain dermatologic conditions.2 Barrier disruption, through both lipid


alterations and elevated surface pH, promotes cutaneous imbalance and makes it more difficult to maintain adequate day to day hydration.2,4


Skin microbiome Architecture and composition The skin is colonized by a diverse set of commensal microorganisms, referred to as the skin microbiome.


November 2025 PERSONAL CARE


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