Commensal microbial communities on the skin, also known as the skin microbiome, do not cause disease and benefit the body. They may be fixed or exist temporarily on the skin.
The skin microbiome interacts with the bodyâ€™s immune system and may affect its functioning. And the immune system regulates the makeup of the skin microbiome.
Aging causes changes to the skinâ€™s structure and function. This may result from â€œintrinsicâ€ factors, such as hormonal, metabolic, or immune system changes. â€œExtrinsicâ€ factors, such as smoking and exposure to sunlight and certain temperatures, may also trigger immune processes that affect the skinâ€™s structure and rejuvenation.
Increased wrinkles, decreased elasticity, reduced wound healing, and impaired barrier function are skin changes that occur during aging. Changes in the skin microbiome can also stem from a decline in the production of sebum, which is an oily substance that protects the skin, as well as from decreased water content in the skin and immune dysfunction.
Age-related microbiome changes
Advanced scientific methods called 16S ribosomal RNA gene and metagenomic sequencing techniques are now available to assess changes in the skinâ€™s microbes caused by aging.
Dr. Elizabeth Grice, an associate professor of dermatology and microbiology at the University of Pennsylvania, explained in a 2019 lecture that the 16S ribosomal RNA sequencing technique allows us to â€œanswer the questions [about] the composition of a sample or the diversity of a sample.â€
She went on to say that â€œShotgun metagenomics provides a more nuanced view of the skin microbiome. Using these methods, one can take a sample containing the genomic DNA, [â€¦] break up that DNA in the sample, and then sequence those fragments. This allows one to identify microbes to the species and strain level, it allows one to reconstruct the genetic and functional metabolic pathways within a sample and, importantly, it gives you a multi-kingdom view of the skin microbiome.â€
Previous studies have demonstrated that the skin microbiomes of all humans consistently contains certain species of Staphylococcus, Cutibacterium, Corynebacterium, and Acinetobacter bacteria.
However, age, body area, gender, and geographic location affect the composition of the skin microbiome. Although previous studies had identified changes in the makeup of the skin microbiome related to aging, researchers had yet to fully understand the mechanisms behind these changes.
In a new study, a team from NIZO Food Research, in the Netherlands, set out to understand the connection between the bodyâ€™s cellular processes, called co- metabolism, and genes, or bacterial functionalities, involved in skin aging. EstÃ©e Lauder, a company that sells skincare products, partially funded the study.
First, the researchers searched existing scientific literature to identify common biologic pathways between humans and skin microbes linked to intrinsic skin aging. They then used 16S ribosomal RNA sequencing testing from cheek samples of female participants with various age-related skin changes to confirm the changes to the skin microbiome composition seen in selected studies.
The team took skin swab samples, one from each cheek, from 25 healthy female participants of European descent in Belgium. The participants fell into two age groups, one aged 20â€“28, and the other aged 59â€“68.
The study excluded participants with certain skin conditions and external factors related to skin aging. Some of the exclusion criteria included:
- use of skin medications, such as antibiotics, antifungals, or steroids, within 1 month of the study
- smoking, or a history of smoking in the past 2 years
- tanning or sunbathing
- drinking more than 3 servings of alcohol per day
Skin aging bacterial pathways
The researchers gathered reference genomes from the gene sequences database of the National Center for Biotechnology Information. The information concerned genes relevant to skin aging, as identified and confirmed by testing.
The team then used microbial pathways to create graphical models, which they used to analyze the reference skin organism genomes, 16S ribosomal RNA sequencing testing, and data from the direct analysis of genomes from the collected skin samples.
The group found that bacterial pathways linked to skin aging were related to the production of ceramides, which are lipids that compose the natural skin barrier, as well as fatty acids and pigmentation. The researchers also determined that bacterial enzymes involved in protein glycation were associated with skin aging.
Protein glycation in the skin occurs when sugars link to proteins, such as collagen and elastin. An accumulation of glycation of collagen and elastin end products can result in loss of skin elasticity and sagging.
Dr. Dina F. Bierman, a board-certified dermatologist at Providence Saint Johnâ€™s Health Center, who was not involved in the study, explained to ishonest that:
â€œ[The study] went one step beyond what we already knew. [â€¦] They separated the population based [on] how their skin had aged. [â€¦] Making that distinction is very important, in terms of understanding how the bacteria and their presence are influencing the skin and the metabolic processes that influence aging.â€
One limitation of the study, however, is its small size and lack of diversity, which may limit the generalizability of its findings. Overall, the results may serve as a basis for future studies seeking to improve our understanding of the interplay of molecular processes and the microbiome in skin aging.
Dr. Bierman described the study as a good starting point, but added that â€œA lot of research [is needed] before we can actually, for sure, say what the different bacteria are doing and how they interact with each [other], too, and might influence how our skin ages.â€