Anne Charpentier – CEO Skinobs
The evaluation of the effect of dermocosmetics or active products on the skin microbiota is evolving into more and more complex models. And yet, these never reach the sophistication of the ecosystem of the bacterial biofilm of the skin. In addition, it is now known that the skin microbiome is subject to intra-individual variations depending on the body areas and inter-individual according to genetic, intrinsic, and environmental factors.
A complex ecosystem deeply linked to the skin homeostasis
Healthy skin promotes an adequate balance of the different bacteria present and vice-versa, skin homeostasis involves a diverse and highly controlled microbiome. Sometimes the simple decrease of one species can benefit others, which then become potentially pathogenic. 2D or 3D models including the inoculation of one or more microorganisms, living, or inactivated, allow to progress on specific problems, such as those associated with dysbiosis such as acne, atopic dermatitis, psoriasis, or scalp disorders… These approaches, which can sometimes be considered “reductionist” as the bacterial ecosystem of the skin is complex, remain unavoidable and contribute to the advancement of knowledge in the fields of skin biology and microbiology. Cosmetics products should preserve the bacterial balance of healthy skin as varied as it may be and allow fragile and injured skin to regain their natural balance.
Since the discovery of the intestinal microbiota, the question of the skin microbiota (micro-organisms, bacteria, viruses, fungi, yeasts), is under every lip. 100 trillion of bacteria are living in our bodies and everybody wants to know more about the impact of the cosmetics use on the skin bacteria ecosystem and how these phenomena can be measured?
The microflora is usually subdivided in 2 groups:
- the transient flora, saprophytic and pathogens microorganisms with Staphylococcus, aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus species…
- The resident flora, pathogenic and commensal microorganisms with Proteobacteria, epidermidis, S. hominis Propionibacterium, Corynebacterium, Dermabacter, Brevibacterium, Micrococcus, P. aeruginosa, Pityrosporum, Malassezia, Demodex…
The balance of cutaneous microflora is dependent of the several conditions of its ecosystem: temperature, pH, hormones, light, UV, lipids, proteins, water… It is mainly influenced by the genetic, the lifestyle and the diet. Each person has their own skin flora composition, distributed from the epidermis until the dermis, which is lifelong qualitatively stable, like a personal microbial footprint. This skin microflora is fundamental for the skin homeostasis and participates to the immune and barrier functions.
Just to remember some definitions, the skin microbiota is defined as all the microorganisms present in the skin while the skin microbiome is a characteristic microbial community that occupies the skin and has distinct physiochemical properties. The microbiome does not only refer to the microorganisms concerned, but also encompasses their activity, forming specific ecosystems. The microbiome includes genetic material, as well as structural molecules, such as enzymes, membrane lipids or polysaccharides. These two terms, “microbiota” and “microbiome”, are not synonymous, since the microbiota refers only to microorganisms, while the microbiome also includes their functional potential.
A paradoxical interest of the beauty consumers for the cutaneous microbiome
The consumers of microbiome beauty products believe that the main benefits of probiotic skincare are balances skin pH, it kills bacteria on skin that causes acne/blemishes, contains live bacteria that fight ‘bad’ bacteria on the skin, keeps microbiome balanced and creates protective barrier on skin surface. Moreover, consumers are gaining interest in the skin microbiome as observed with an increased of 68% average annual growth in product launches with microbiome claims from October 2018 to September 2023 (Innova Market Insights).
Microbiome claims, the era of a new revolution for the cosmetics?
Currently, the approach of supporting microbiome claims is becoming increasingly important for assets, finished product and brands. Thus, growing the interest of in-depth analysis of the interaction between the product, skin and microbiome and their mechanisms of action. Many testing laboratories (+80 CROs worldwide) are studying these new claims looking in the direction of the metagenomic field. The studies of the cutaneous flora are complex, and it is not always easy to understand its functionalities and interactions with the skin metabolism. The first way is to analyse the genome of the bacteria of the skin flora. It is a living layer of the skin to be discover like a new continent of the body.
First, we must consider that the skin microbiota does not belong to the epidermis layer of the skin. It is a “foreign” substance of our body:
- acting as a resident of the skin and
- forming a biofilm at the epidermis surface
- maintaining the good conditions of the skin and regulating inflammation,
- protecting the body from the aggressive environmental conditions and various internal stresses.
Various bacteria disorders might be considered as a source of cutaneous dysfunctions like acne, eczema, dandruff or atopic dermatitis modifying this precious balance.
The cosmetics search for 3 main benefits:
- the rebalancing, pro-biotic, pre-biotic
- the probiotic-like
- the anti-microbial effects.
In a regulatory approach, the first thing is that the personal care targeting the skin microbiota must be safe following the EC 1223/2009. At the European level, the debate on the regulatory status of “microbiotic” cosmetics was initiated in 2018. Work still underway within the International Cooperation on Cosmetics Regulation has resulted in a document on definitions relating to the microbiome in cosmetics (published in June 2022).
| Probiotics | Defined as viable microorganisms (active or dormant) added to a cosmetic product and intended to provide a cosmetic benefit to the host at the site of application, either directly or through an effect on the host’s microbiome. Active microorganisms are defined as growing organisms that increase in number and/or biomass. Dormant microorganisms do not grow, but retain their metabolic activity. |
| Postbiotics | Are inanimate ingredients of microbial origin added to a cosmetic product for cosmetic benefit. These components can be cells or cell fractions, a fermentation filtrate, or a metabolite of a microorganism. |
| Paraprobiotics | a subgroup of postbiotics, are ingredients derived from inactivated probiotic microorganisms added to a cosmetic product with an anticipated cosmetic benefit. Paraprobiotics can be inactivated microbial cells or components of cellular structures, with or without metabolites |
| Prebiotics | are substrates added to a cosmetic product to be used by the host’s microbiome, with an expected cosmetic benefit for the host |
Cosmetics and personal care products must include in their formula only prebiotics, probiotics and postbiotics ingredients that are not listed on the Annex II of the prohibited substances. Moreover, each brand must assess that the microorganism involved in the formula do not produce any toxin. Claims such as “Microbiome friendly”, “Respect microbiome”, “maintains the microbiome” or “microbiome safe” should not be misleading and must not imply that it improves the skin microbiome. Cosmetics are allowed only to keep the skin healthy and are not allowed to make it healthy or to modify the physico-chemical processes of the epidermis. Personal care, toiletries or cosmetics claiming that they support and protect the skin microbiota are allowed using claims such as supports or protects the microbiota, microbiota friendly. But these products cannot claim that they stimulate, boost, reduce, or improve the microbiota or its diversity even it is admitted that higher diversity is linked with higher hydration, and less infected skin.
How to evaluate cosmetics activity on the skin or scalp microbiota
Understanding the interplay between skin, microbes and their variations due to cosmetic application is essential. Cosmetic activity on skin microbiota can be evaluated in different settings, in vitro lab testing, ex vivo and directly from human skin samples. In vitro tests allow the experimental conditions to be strictly controlled providing a brief snapshot of how the product interacts with isolated bacterium strain by strain or mixed of strains. The assays conducted on 3D skin models such as full thickness (epidermis and dermis layers) can allow to study the behavioral aspects of bacteria and how tissues react to the presence of these bacteria. This approach offers reliable results while avoiding variations due to the individual differences of each person. However, they propose a narrow view and do not analyse bacteria withing its natural context. Moreover, since only small fraction of microbes forming the skin microbiota could be cultured using standard techniques, skin microbiome research relied heavily in culture-independent metagenomic analysis. While these methods are highly sensitive and efficient for identifying the composition and relative abundance of microbial communities, they fall short in elucidating molecular interactions and the functional roles of bacterial metabolites in host-microbe dynamics. A significant advancement in skin microbiome, TUS Skin Bacteria Co-culture medium, introduced by Yamamoto et al. (2024) enabled the in vitro co-culture of four key skin microbes—Staphylococcus epidermidis, S. capitis, Cutibacterium acnes, and Corynebacterium—by replicating the skin’s natural environment and allowing to use microbial species collected form human volunteers in with culture-dependant techniques.
Finally, in vivo human testing gives a broader view of the microbiome, analysing microbes within their natural context and allowing longitudinal analysis (evaluate the product over time and its impact on the microbiome). Multiple factors are important in the implementation of in vivo skin microbiome studies, from study design, sample collection, sample processing and the incorporation of bioinformatics to delineate potential cause/association from sequencing results. As the important intra-individual diversity of the cutaneous flora is also associated with a high level of inter-individual variability, study population and study design are of extreme importance. Sample collection methodologies include swabbing, tape stripping, biopsies and now a days companies are even proposing self-sampling at-home collection kits (e.g Sequential; Smart ProbesTM, Hellobiome…). Protocols focus on comparing skin swabbing of the treated zone and of the non-treated or placebo zone, before and after treatment.
Sample processing includes simple quantitative techniques CFU counting, and quantitative methods at molecular level such as qPCR and rRNA gene sequencing which is the most common approach for analysis of composition of microbial communities. rRNA sequencing is based on high-throughput sequencing of PCR amplicons for prokaryotic communities (16S V4, V1-V3), eukaryotic communities (18S), fungal communities (ITS2), and archaeal communities (16S V4-V5). While techniques such as PCR provide a fast identification of known sequences, next-generation sequencing (NGS) offers a broader insight since it is a hypothesis-free approach providing a tool to detect novel genes with higher sensitivity. Shotgun Metagenomics which includes NGS 16S rDNA or ITS that allow to look at all the genes of all the microorganisms in a sample allowing to assess microbial diversity and detect the abundance of species under different conditions.
While metatransciptomic sequencing employs various NGS platforms to uncover how genes are activated in response to lifestyle, environment & treatment evaluating the effect of a product on skin-related microbial gene expression. The integration of multiple layers of biological data, including genomics, metabolomics and proteomics also known as multi-omics, provide a more comprehensive understanding of how products impact both the human body and its microbiome. To do so, the exploitation of metadata to perform bioinformatic/biostatistics analysis to delineate potential cause/association with sequencing results of great importance. For example, HolXplore (Phylogene) which is a complementary analysis of data from meta proteomics experiments, allowing to highlight the biological effects associated with the results. Other suppliers that utilise database for analyses pipeline include Byome Labs, Sequential, BIO-ME and Hellobiome.
Several laboratories have created in-house certifications such as “microbiome-friendly”, “respect the microbiome, “kind to biome” and “maintains the microbiome” to help brands communicate about how their products do not harm the skin microbiome. Each company uses a combination of in vitro and/or in vivo protocols to mainly ensure that a given product does not have a detrimental effect in skin microbiome. At the moment there are no specific global regulations in place for skincare products or ingredients targeting the skin microbiome, however the cosmetics industry has to follow the regulatory for standard cosmetics regarding safety and claims. Hopefully, one day further regulatory approaches will lay the grounds for to harmonize communication in the novel area of cosmetic science.
combining point of expert’s view on clinical evaluation perspectives
A lot has happened since she first wrote about the Microbiome, back in 2012. Small brands have rushed in, large ones, not so much, but there is a lot of activity on the dermo brands front, and the premium consumer side is slowly starting. So why are premium brands so timid in using the Microbiome argument? The Skin Microbiome analysis is still young. It is a discipline that is still in its infancy. Especially in Skin Care. Sampling is still complicated, following up is a nightmare. Lifestyle impacts the Microbiome as much as genetics does. The liminal nature of the “organ” complicates matters a great deal. So, yes, there are a lot of claims, many of them implying things that we just cannot be sure of. Yet. What we need, before we speak with the consumer, is industry-wide guidelines and consensus. If understanding what is happening on the skin with the microbiome analyse remains complex despite the presence of excellent testing labs in the space, one thing would help a great deal: understanding the impact of the products before they are formulated. Let‘s make it routine to test the raw materials for their microbiome impact before the regulator makes us.
Skin is a rather hostile environment, salty, dry, and poor in nutrients. Certain parts remain however moist and lipid rich propitious to bacteria blooming. As the skin matures with age, notably during puberty where hormones are kicking-in and triggering a cascade of physiological and physical transformations, the skin microbiome is constantly evolving until adulthood. On average, a person has around 1,000 species of bacteria on their skin offering a variety of distinct ecosystems, which create conditions that favor different subsets of organisms.
Researchers have uncovered extensive communication between bacteria, skin cells and immune cells. These interactions have been described in plethora of physiological functions as in skin barrier reparation, limitation of trans-epithelial water loss and defences against infections. Deciphering the role of skin bacteria functions is a tremendous work and this domain remains however poorly understood. Functional analysis and deciphering mechanisms of actions of bacteri /microbes are a prerequisite to better understand their role and activities. Skin is an accessible and untapped reservoir to dissect and improve the comprehension of host- microbiome interactions. Furthermore, an extensive analysis of the skin and its microbiome via specific protocols using mass spectrometry proteomics and dedicated bioinformatics pipelines are keys to both decipher functional correlations and mechanisms of actions between skin and its microbiome.
For optimum beauty products results, every cosmetics product should follow the approach of fostering the natural homeostasis of skin and hair instead of imposing additional stress with aggressive chemicals. This is achieved best by exclusively high-quality ingredients that enhance the microbes dwelling on the skin. The skin’s microbiome differs significantly between the various body parts. To make sure a product does not harm the microbiome, some testing laboratories have developed different standards: face and body; scalp; infant skin; private parts; foot….
Also, cosmetics claims that are attributed to microbiome skin or scalp care can be easily assessed by using classical biometrological methods objectivating pH balance, Hydration, Barrier fonction, Trans Epidermal Water Loss, blemishes, irritation, inflammation, sebum and lipids, Skin turn-over and desquamation, sensitivity, or dandruff. The Skinobs Clinical Testing platform allow you, for free, to easily find all methods selecting a specific claim.
The beneficial anti-ageing effects of probiotics are now widely reported. A recent study has proved their significant anti-ageing effect by increasing the skin water content, the skin elasticity, the skin gloss and decreasing transepidermal water loss as well as the wrinkle depth. The analysis on skin microbiome performed by PCR technology could be a valid support for objectifying the action of probiotics.
The future of skin microbiota evaluation
There is no ideal composition of the skin microbiota as people are living in different ecosystems and have various lifestyles. Scientists agree that among the huge inter- and intra-individual variation, a wide variety of microbiota species assure a good health. This bacteria ecosystem synthetizes a myriad of elements which have an important metabolic activity for our skin health. It could be necessary to protect, to rebalance and activate it on the cosmetics side. Simply said the aim for personal care could be to reduce the “bad” bacteria and protect the “good” ones! But the notion of “bad” or “good” is relative depending of the physiological state of the skin. Now things are not so simple!
In 2025, the beauty industry is evolving significantly in an increasingly connected, digitalized, personalized world where social networks impact the beauty routines. In response to the expectations of these new consumers searching for “microbiome activity”, cosmetics brands are developing personalization by specific microbiota analysis essential for the microbiota centric product recommendations. With the advent of digital technologies, the miniaturization of measurement tools, A.I and data analysis, this “personalization” of “microbiota” cosmetics care is reaching sophistication thanks to the development of swabbing and analysis.
It is regrettable, however, that the data collected so far are generally on Caucasians populations, even if specific developments are made on specific ethnic groups, particularly Asians. The need for inclusivity in the beauty world is there and the approach to skincare targeting the microbiota should follow this global trend.
Regarding the in vitro evaluation, the development and use of 3D skin models could offer invaluable insight into how cosmetics affect the skin microbiome in a controlled, replicable environment, deepening our understanding of host-microbe interactions at the skin.
In conclusion, the microbiota will play a key role in the cosmetics of tomorrow. We move towards personalized and preventive cosmetics. Claim substantiation will evolve with the regulation and the products development. We must keep in mind the diversity and the balance of the skin flora in the future developments of actives and personal cares. May be one day we should measure their impact of on the microbiota before launching the products on the market.
References
Kromidas, L. et al. Skin Micorbiome- and infromational Guidance for the Personal Care Industry. IFSCC. 2024; 27(1):71-81
Mim MF et al. The dynamic relationship between skin microbiomes and personal care products: A comprehensive review. Heliyon. 2024 Jul 13;10(14):e34549.
Van Belkum, A. et la. Being friendly to the skin microbiome: Experimental assessment. Front. Microbiomes 1:1077151.
Kong H. H et al. Performing Skin Microbiome Research : A Method to the Madness. J. Investi Dermatol. 2017; 137:561-568
Yamamoto, I. et al. Developing an In vitro Culture Model for four Commensal Bacteria of Human Skin. AATEX. 2024; 29(1):1-7
Leng, J. et al. At-Home, Self-sampling of the skin microbiome: development of an unsupervised sampling approach. Microbiology Society. 2025
Carvalho MJ, et al. Skin Microbiota and the Cosmetic Industry. Microb Ecol. 2023 Jul;86(1):86-96.
Cosmed: https://www.cosmed.fr/cosmetiques-et-microbiome-un-cadre-reglementaire-en-construction/
CONTACT
Anne Charpentier + 33 (0) 6 30 08 90 98
Email : acharpentier@skinobs.com
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