Cutaneous microbiota composition could be a relevant marker of skin aging

During skin aging process, physiological changes (decrease in sweat, sebum and the immune functions resulting in significant alterations in skin surface physiology including pH, lipid composition and sebum secretion) provide potential alterations in the skin ecology that may affect the skin microbiota.

In order to assess the effect of aging on skin microbiota, a recent study by Shibagaki et al was conducted in two different age groups (21–37 years old/60–76 years old) of 37 healthy Japanese women. It showed that:

• The species richness is significantly higher in the older group
• There are global taxonomic differences in the skin microbiota with, in the older group
  • A significant lower abundance of Actinobacteria, notably of genus Propionibacterium, (cheek, forearm, forehead)
  • A significant higher abundance of Proteobacteria (forearm, scalp), Firmicutes (forehead) and Bacteroidetes (forehead, cheek)

These alterations could be explained by less nutrients available on older skin due to the decrease in skin cells renewal and sweat and sebaceous functions, and by weakened immune system.

In addition, the investigators identified the 38 species largely contributing to differentiate the skin microbiota of the two age groups, most of which were significantly overrepresented in the older samples and included many normal bacteria frequently detected in the oral cavity. This finding suggests that:

• Oral normal bacteria largely contribute to bacterial diversification and alteration in the older skins.
• Aging-related diversification of skin microbiota is correlated with changes in skin physiology that depend (i.e., sebum level, pore density, skin elasticity, etc.) or not (i.e., photoaging, etc.) upon aging.

Lastly, the authors concluded: “skin microbiomes could be used as a new indicator to quantify skin age irrespective of their chronological age. As a significant correlation between taxonomic and functional diversities has been reported, elucidating functional features specific to older skins by metagenomics and metabolomics will be valuable to more deeply understand aged skin for development of new approaches to prevent skin disorders that specifically occur in older skins.”