SKIN MICROBIOME
In summary, the barrier function of the skin, supported in part by microbiome activity, operates at multiple levels: competitive exclusion of pathogens, antagonism via antimicrobial peptides and other inhibitory molecules, support for the production of key lipids such as ceramides, and immune signaling oriented toward effective local defence.2,6,8,10
Link between the skin microbiome and ageing Composition across the life course Figure 1 shows that it is not sufficient to oppose children and adults in study models; additional categories should be distinguished, namely newborn, infant, child, adolescent, adult, and senior, and sex should be taken into account. Taxonomically, skin ageing is frequently
associated with a decline in Cutibacterium, consistent with reduced sebum secretion, and with higher relative abundances of Corynebacterium, Acinetobacter, Streptococcus, and Prevotella in older subjects.12
Overall, the
literature reports higher diversity and greater variability among older individuals, a trend that should be confirmed in multiethnic studies that account for sex specificities.11
Bidirectional mechanisms As skin ages, surface pH tends to rise, sebum production decreases, and tissues are remodelled. These changes alter the microbial environment and are often accompanied by a decline in Cutibacterium and, at times, commensal staphylococci, while Corynebacterium and certain Proteobacteria become more prevalent. These population shifts in turn drive age related changes in skin physiology.2,4 The influence also operates in the opposite
direction. When C. acnes becomes scarce, fewer sebum derived fatty acids, including propionic acid, are available to maintain a naturally acidic surface pH, which therefore tends to increase. Likewise, if S. epidermidis is less abundant, the skin benefits less from its sphingomyelinase that supports ceramide production, and TLR2 activation by this species less effectively stimulates AMP production and the strengthening of tight junctions, leading to a more fragile barrier. Certain metabolites from S. epidermidis
may also shape local immunity by recruiting T lymphocytes and supporting keratinocyte proliferation. In sum, microbiome composition can in turn affect surface pH, hydration, and barrier integrity in mature skin.8-10
Implications for mature skin The higher alpha diversity described in older skin indicates a more heterogeneous ecosystem that is potentially less stable, in which opportunistic species can persist more easily when the barrier is weakened.5,11 Added to this are changes in pH, reduced sebum, a decrease in Cutibacterium and Staphylococcus, and an increase in Corynebacterium and various Proteobacteria; dysbiosis profiles are therefore more frequent in older individuals. These microbial shifts may accelerate certain age related skin changes, reinforcing the vicious circle in which mature skin and the microbiome co influence one another.2 In this context, preserving the skin
microbiome is essential for maintaining skin health, as it supports barrier integrity, protects against pathogens, sustains hydration, and enhances long-term resilience.2,5
Solutions and future perspectives — microbiome friendly approaches and microbiome studies 1. Strategy Preventing and correcting signs of ageing relies on restoring the skin barrier and reducing exposome factors such as ultraviolet radiation and oxidative stress, through a combination of antioxidant containing products and daily photoprotection. This approach limits dysbiosis and supports barrier resilience in mature skin. In this context, incorporating prebiotics,
probiotics, and postbiotics into care for mature skin is considered a lever to strengthen barrier function, modulate inflammation, and improve tolerance to ultraviolet exposure and oxidative stress, while supporting the stability of commensal communities.2
2. Targeting microbiome functions hydration, pH, and immune defence Within the cutaneous ecosystem, key commensals perform beneficial functions that can be directly leveraged by formulation and care routines: ■ Hydration: supporting the population
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www.personalcaremagazine.com
November 2025 PERSONAL CARE
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