ALBERT DASHI, PHD¹, PETRONILLE HOUDART, DPHARM², OLIVER WORSLEY, PHD³

1. CSO and Co-Founder at Sequential Skin Ltd
2. Skincare Director and Co-Founder at Sequential Skin Ltd
3. CEO and Co-Founder at Sequential Skin Ltd

The skin microbiome consists of an organic ecosystem of trillions of bacteria, fungi and other microorganisms that act as a natural barrier, interacting with one another, defending against potential pathogens and contributing to the skin’s overall health and resilience (1). [GC1] The microbiome of every individual is entirely unique, shaped by their external environments as well as the substances they are exposing their skin to. The microbiome can be impacted by factors such as stress, pollution, personal care products and even the countries within which we reside.

Due to increased knowledge on the microbiome, respecting its delicate balance has become paramount in formulating effective and innovative personal care products. It is known that when the skin microbiome is in dysbiosis (when microbial diversity is imbalanced), it can lead to skin conditions such as rosacea, acne, atopic dermatitis, and many others (2).

The microbiome has become a central consideration in the development of skincare solutions, representing a transformative shift towards products that not only enhance the appearance of skin but also contribute to the overall health and well-being of it (3). The vast majority of key players in the industry have understood that the microbiome is not just a trend that will dissolve in a few months or years, it is an important component of medicine, which will impact every field of human health, and relating to personal care.

A significant portion of the discourse surrounding the question of whether microbiome certification is even necessary stems from the wording of the certifications themselves. The industry has begun to adopt terms such as “microbiome-friendly” and “biome friendly,” without full research being carried out in understanding these human-related microbes, using sophisticated technology such as Next Generation Sequencing.

The scientific community that is driving the research within the area are beginning to express the view that these words hold little meaning and inaccurately represent the complexity of what is occurring in the microbiome. On the other hand, industry thought leaders are seeking to simply educate their consumers to lower the barriers to entry. Both the science and the education of consumers is imperative for the microbiome movement to make headways, but the varying approaches to the science and its explanation has resulted in certifications of different calibre.

There are those who are marketing their products as having microbiome benefiting results without doing any testing, highlighting ingredients that have been found to balance the microbiome. Unfortunately, due to lack of proper data to support their claims, such brands can find themselves under major scrutiny, especially in the North American market where false claims can result in legal repercussions as was seen with a large FMCG’s portfolio company in 2021. The best solution to this problem is to pick the correct testing to support claims.

In the realm of scientific research and product development, the importance of testing methodologies cannot be overstated. When it comes to understanding the intricate world of bacteria and microbes, there are numerous testing methodologies that are currently being adopted by the industry: in-vitro, ex-vivo, and in-vivo.

in vitro Microbiome Testing: is conducted in a controlled, artificial environment such as a lab and typically focuses on isolated bacterial strains to assess interactions between the product and the isolated bacteria. Although it can allow for precise examination of how a bacteria responds to products, it neglects to take into account the complex and dynamic nature of the microbiome as a whole. This form of testing can be crucial within the context of medicinal research, where it might be crucial to understand the relationship between a treatment product and a pathogenic bacteria that could not otherwise be tested safely in human subjects. It can also serve well for more upstream analysis, when working with raw ingredients that are still undergoing exploration before they are infused into formulations. However, when it comes to the microbiome, there is still little evidence to support that in vitro approaches carry sufficient data to back microbiome claims in human.

ex vivo Microbiome Testing: involves the study of the microbiome outside of its natural living context by using skin samples and intact tissue. This enables the examination of microbiome responses to products in a controlled yet biologically relevant setting. It is viewed as a middle ground between in vitro and in vivo. The limitation are often: access to tissue; batch effect with the tissue of origin; difficulty in co-culturing methologidies (the same microbes we’ve traditionally tried to remove from cell culture with antibiotics!); and finally, difficulty in longer term viability in culture, for longitudinal studies on the skin.

In vivo Microbiome Testing: is conducted directly on human skin, providing insights into the behaviour of the microbes in their organic environment and offering a thorough understanding of microbial interactions. This type of testing allows for a proper assessment of a product's impact on the microbial balance and diversity as well, something that cannot be accomplished with other forms of testing. However, as with all methodologies, there are a few limitations when it comes to the in vivo approach. For starters, there is still much research to be carried out in order to fully characterise the multitude of strains, and more importantly, the interaction of these microbes with themselves – and us, their host. There are also debates concerning the extraction of microbes and how to determine whether they are dead or live upon collection and what this means functionally. There is considerable R&D that is being pushed on this side to minimise the ambiguity through the use of qPCR approaches for both DNA (what’s there) and RNA (what is active), henceforth, there is still much to uncover but the in vivo method still provides the best confidence of what is occurring in human.

Despite the numerous certifications gaining traction within the industry, the key to understanding whether or not it holds any weight and value stems from what hypothesis it is trying to test. In order for a product to be tested and certified with any confidence, the answer to the following four questions are crucial:

1. Is there any significant change in the total microbial diversity before and after product usage, longitudinally?
2. Does the product alter the balance of commensal to opportunistic microbes?
3. Are there predictive functional and metabolic changes, from the microbiome profile, that are maintained or changed after product usage?
4. Can we associate any significant biophysical changes (e.g. pH, hydration, elasticity) or meta-data (e.g. dermatology assessments, treatment, imaging, age, ethnicity) with specific microbial changes?

Unfortunately, unless a product is evaluated on live human skin, these answers cannot be discovered, nor have in vitro tests been reliably validated against in vivo or clinical microbiome tests. The total diversity of the skin microbiome can only be measured when taking a sample from human skin and quantifying it. Unlike in vitro and ex vivo models of testing, the in vivo approach offers relevant data that can be extrapolated to the general population and translated into sound claims.

Studying Impact on Atopic Skin

When testing on human subjects, there is a huge opportunity to test products formulated for specific skin conditions to see how they will interact with those individuals' unique microbiome. The personal care industry is often driven by the need to problem solve consumer concerns, creating formulations that will target specific niches. If a brand is looking to test a product designed especially for acne-prone skin, recruiting individuals with this skin concern is the only logical step in uncovering whether or not their product will help their condition and support their microbiome. These are considerations that are overlooked when going the in vitro route. Indeed, in studying conditions like atopic dermatitis, there have been key strains involved in the inflammatory process, and likelihood of flareups. Something that requires strain-level analysis in vivo to uncover.

Long-term Effects of Formulations

in vivo Human testing allows for longitudinal analysis (evaluating usage of the product over time), giving deeper insights into a product's impact on the microbiome rather than a brief snapshot of how the product interacts with an isolated bacteria. A well structured study should be centred around multiple sample collection points, giving significant time to pass between collections. This allows brands to review how a product is performing before and after usage, but also take into account its gradual impact on the microbiome.

Measuring Products Against Control Groups

Human testing provides an additional advantage by allowing the evaluation of formulations containing active ingredients in comparison to control groups. This expands the breadth of the study, illustrating the effects of an active ingredient or its concentration in a product when contrasted with a group that is exposed to a basic formula. This approach enables a more comprehensive understanding of the formulation's influence on microbial balance and diversity.

Expanding the Scope of the Study

Although the microbiome is gaining traction on the research and development side of the industry, the consumers of skincare and personal care products are still seeking solutions to their primary concerns: acne, rosacea, atopic dermatitis, skin elasticity loss, etc. This is why a human approach to testing the microbiome brings forward the opportunity to evaluate it against other metrics, such as biophysical aspects such as skin hydration, elasticity, pH, etc. Unlike isolated lab testing, in vivo microbiome testing can be used for correlation analysis between other areas and the microbiome.

The costs associated with microbiome testing for consumer personal care products is an important one to take into account. In vitro testing stands as the more cost-effective approach and limits the factors needed to take into consideration when setting up a study. However, it is important to realise that this level of testing and the certification associated with it might not be robust enough when regulations are put into place where the microbiome is concerned.

On the other hand, the in vivo approach can lean on the pricier side, there is significant research to support the claims being put in place and the certification that accompanies it. With the need to test on human subjects, recruitment and analysing the microbiome against other biophysical elements, the costs associated rival clinical studies with the promise of relevant data that will hold value over time.

The personal care industry is currently grappling with a notable absence of comprehensive regulations, leaving a void in oversight and accountability. This lack of framework has raised concerns regarding the consistency and reliability of product claims, potentially exposing consumers to uncertainties about the efficacy and safety of microbiome-based formulations (4). Without standardised guidelines, there will remain a risk of misleading marketing practices, allowing for the proliferation of products that may lack scientific validation or adhere to established quality standards. The absence of regulation poses a challenge not only in ensuring consumer protection but also in fostering a trustworthy and transparent marketplace for microbiome-related personal care products. As the industry continues to evolve, addressing these regulatory gaps is becoming essential to safeguard both consumer interests and the integrity of the products entering the market.

In conclusion, the necessity for regulations in the microbiome certification of personal care products remains an important discussion. However, amidst the ongoing need for regulatory frameworks, there exists an opportunity for brands to make informed choices. Armed with a better understanding of the essential components that constitute a robust study, brands can select certifications that align with the academic calibre of clinical studies. This not only enhances the credibility of their marketing claims but also contributes to the establishment of industry standards that prioritise both consumer well-being and scientific rigour in the evolving landscape of microbiome-focused personal care.