To continue the 'Skin Microbiome' series where we previously discussed skin microbiota and the application of metagenomics in studying this field, this post will introduce a scientific article that sheds light on how scientists have utilized metagenomics to investigate questions related to the skin microbiota. By examining the methodology and findings of this study, we can gain a comprehensive understanding of the intriguing realm of the skin microbiome and its implications for skincare and cosmetics.
The article, titled "Changes of the human skin microbiota upon chronic exposure to polycyclic aromatic hydrocarbon pollutants", was published in the Springer Nature Journal in 2020, and you can read it by clicking on this link. The study was conducted as a collaborative research project, combining metagenomics and metabolomics, with the aim of investigating the microbial community present on the skin of individuals exposed to polycyclic aromatic hydrocarbon (PAH) pollutants in two major cities in China. This research project is particularly captivating due to its contributions towards our comprehension of the interplay between air pollutants and the skin microbiome, as well as the application of “omics” technologies in skin research.
This post is structured into three main parts, aiming to provide a comprehensive overview of the article, its implications for future research, and the significance of active ingredients in the cosmetic market:
Analysis of the scientific article: We will look into the main ideas of their research project, briefly covering its methodology, findings, and implications so as to acquire a deeper understanding of the effects of chronic exposure to PAH pollutants on the human skin microbiota.
What should we do to protect the skin microbiome from PAH exposure?: After understanding the impacts of pollution on human skin microbiota, this part would provide suggestions for some tips to maintain a healthy skin microbiota for an improved skin barrier.
Active ingredients available in the cosmetic market: In addition to analyzing the research, we will review the active ingredients currently available in the cosmetic market and their potential benefits for skin health. By understanding the active ingredients present in skincare products, we can make informed choices when selecting products that promote a healthy skin microbiome.
Okay, let's get started.
1/ Overview of Research Project:
Background information
Air pollutants can enter the human body through inhalation, ingestion, and dermal absorption. Polycyclic aromatic hydrocarbons (PAHs) are a group of toxic compounds commonly found in sources such as vehicle emissions, industrial pollutants, and cigarette smoke, which contribute to the constant presence of PAHs in polluted air. These compounds have been associated with various adverse health effects, including skin-related issues. Chronic dermal exposure to PAHs, for instance, is known to contribute to premature aging and other common skin diseases.
To evaluate the changes in the skin microbiome before and after exposure to PAHs, researchers employ metagenomic techniques. As a brief reminder from previous posts, metagenomics involves the analysis of genetic material extracted from a sample to study the composition and function of the microbial community present. By utilizing both amplicon sequencing and shotgun metagenomics, comprehensive insights into the skin microbiome and its response to PAH exposure can be obtained. Amplicon sequencing targets specific genes or regions of microbial DNA, enabling targeted analysis of particular bacterial groups or functional genes. Conversely, shotgun metagenomics involves sequencing all the genetic material present in a sample, providing a more comprehensive view of the microbial community and its functional potential.
This collaborative research project successfully identified changes in the abundance, diversity, and functional capabilities of the skin bacterial commensals following PAH exposure in Chinese citizens residing in Baoding and Dalian. The findings from this research enhance our understanding of the interactions between the skin microbiome and environmental pollutants, specifically PAHs, potentially leading to the development of strategies to mitigate the harmful effects of PAHs on the skin and enhance the beneficial activities of commensal bacteria in pollutant degradation.
Experiment design
A total of 204 Chinese women who had resided in two cities in China for more than 15 years were included in the study. The cities selected for the study were Baoding, characterized by high levels of pollution, and Dalian, characterized by relatively lower levels of pollution. All participants were non-smokers, and their health status, medical history, and daily habits were recorded.
Hair samples from the participants underwent chemical analysis for Polycyclic Aromatic Hydrocarbons (PAHs), and based on the results, they were classified into eight groups with similar numbers of individuals and distinct levels of PAH concentration between the groups. While the taxonomic profile and structure of skin and scalp samples from all individuals were analyzed using amplicon sequencing, only those in the lowest PAHs and the highest PAHs concentration groups were further analyzed for community functions through shotgun metagenomics. The aim of the study was to evaluate the effects of pollutants, represented by PAH exposure levels, on the human skin and scalp microbiome.
Results and discussion
In general, these findings underscore the impact of pollutant exposure on the skin microbiota. The study revealed noticeable changes in the diversity and abundance of microbial taxa, along with alterations in the microbiome functions. These changes may have implications for the ability of the commensal microbiota to protect the host against pathogens and maintain skin homeostasis.
Skin site, skin type, and cohort location exhibited a complex interaction that has an impact on shaping the microbial community
As a natural mechanism for protecting against a heavily polluted city, diversification, and taxonomic enrichment were observed among certain rare skin bacteria regardless of skin and scalp types. These bacteria, namely Micrococcus, Paracoccus, Ralstonia, Novosphingobium, and Aestuariimicrobium possess the ability to degrade polycyclic aromatic hydrocarbons (PAHs) and related xenobiotic compounds.
There was an association between skin conditions and the integrity and stability of the microbial network
In addition to skin site and cohort location, the type of skin (healthy vs. acne-affected cheek or healthy vs. dandruff-affected scalp) may be also related to the connectivity and stability of the microbial network. Specifically, studies have shown that skin sites with acne and dandruff exhibit reduced network structural stability, which is associated with a decrease in microbial network integrity. This reduction in stability and integrity is often seen in individuals with skin disorders or adverse skin conditions. Conversely, a robust and stable microbial network has been linked to the maintenance of cutaneous health.
The presence of a stable network indicates a healthier state of the skin, as it is associated with a balanced and diverse microbial community. Therefore, the stability and integrity of the microbial network play a crucial role in determining the overall health and condition of the skin.
Relationship between specific PAHs, microbes, and their metabolites???
Based on the results from the experiments and previous studies, the researchers have put together a conceptual mechanism to elucidate the possible effects of specific PAHs on the skin microbiota or specific microbes and overall cutaneous health. PAHs can reach the skin through various means such as direct contact, exposure, or even through the systemic circulation following inhalation or ingestion. Irrespective of the route of entry, the measured concentrations of PAHs were observed to correlate with changes in the abundance of commensal species.
Furthermore, specific PAHs exhibited varying relationships with certain microbiota and their impacts on skin health. Two major results on the correlations were found in this research:
A significant negative correlation between:
M. luteus and two specific PAHs (fluoranthene and benzo[b]fluoranthene):
Previous research has implied that M. luteus may play a role in protecting the skin against ultraviolet (UV)-induced DNA damage. Considering these findings, it is plausible that the DNA damage induced by PAH exposure could potentially be influenced or mediated by the skin microbiota.
A. johnsonii and phenanthrene:
Exposure to PAHs may lead to a reduction of commensal colonizers and any potential protective effects provided by these commensals against pathogen colonization.
A positive correlation between:
The oral bacteria Actinomyces viscosus and two specific PAHs: benzo[k]fluoranthene and acenaphthylene.
Because the abundance of oral bacteria is linked positively to atopic dermatitis and there is a positive correlation between PAH exposure and oral bacteria, it may suggest one potential mechanism by which PAH exposure may contribute to atopic dermatitis, skin disorder and aging through the accumulation of oral bacteria on the skin.
These findings raise intriguing questions about whether the accumulation of oral bacteria is indeed linked to premature skin aging??? Further investigations are warranted to explore this question in depth.
Staphylococcus epidermidis (a commensal bacterium) plays a crucial role in protecting the host from the colonization of external species, preventing the development of pathogenic traits, facilitating wound healing, and protecting against the growth of skin tumors. Due to the numerous protective effects exerted by this commensal species on skin physiology, it is important to conduct a more thorough and expanded investigation to examine whether PAH exposure is also linked to the abundance of this protective commensal.
The researchers also showed that the detected levels of PAHs were found to be associated with changes in the abundances of microbial genes involved in various metabolic functions.
Because the specific functions of microbial pathways’s metabolites in skin physiology were not well understood, this research paves the way for further research on how PAH exposure could influence the interactions between host and skin microbiota along with their metabolism, particularly in relation to conditions like atopic dermatitis.
Complete or partial PAH degradation led to different effects. While the skin microbiota can potentially degrade PAHs into harmless products, the partial metabolism of PAHs may produce intermediate metabolites that could be toxic to both host tissues and DNA. Additionally, the composition of the skin microbiota is greatly influenced by the physicochemical properties of the skin surface, therefore, it is important to gain deeper insights into the chemical makeup of the skin after complete and partial degradation of PAHs and other pollutants and see how PAH metabolism impacts skin microbiota.
Besides the intriguing findings of this study, it sets the stage for further research to address certain unresolved issues. By gaining a better understanding of the detrimental effects of PAHs on human skin health, this study also serves as a guide and inspiration for the development of innovative active ingredients aimed at mitigating or minimizing the negative impacts of PAHs. This, in turn, can help restore balance to the skin microbiota and promote a healthy microbial community as a protective skin barrier. Furthermore, it is crucial to address the pressing issue of researching and improving the environmental quality to eliminate its adverse effects on human health. Since PAHs have negative impacts on skin microbiota or human health, it is necessary not only to create a protective shield for skin microbiota but also to reduce the presence of PAHs as a representative pollution. Therefore, this underscores the importance of comprehensive efforts to minimize exposure to harmful substances and promote a healthier environment for everyone.
2/ What should we do to protect the skin microbiome from PAH exposure?
Here is the question all of you would probably ask after going over the first section: What exactly can we learn from this study, aside from their scientific contributions to skin research?
PAH is harmful for skin health, and from the most major findings of this research project, long-term PAH exposure definitely has a negative effect on our skin, starting with the change in the skin microbiome. As a product of industrialization, air pollution is increasing and with that, constant PAH exposure is inevitable. So, is there anything we can do to prepare our skin microbiome for everyday PAH exposure, and to improve our overall skin health to combat PAH as well as other air pollutants?
Using cosmeceuticals that contain active ingredients with the ability to protect the skin against pollution is one of the common ways to maintain healthy and aesthetically-pleasing skin. Cosmetics products can play a role in providing nutrients or supporters for development of beneficial skin microbiota such as probiotics, prebiotics and postbiotics. Let’s briefly summarize probiotics, prebiotic and postbiotics and their roles in skin microbiota. Probiotics are live microorganisms that, when applied topically, can help promote a balanced and diverse skin microbiota. They contribute to the overall health of the skin by supporting beneficial microbial populations and inhibiting the growth of harmful bacteria. Prebiotics, on the other hand, are substances that serve as food for the beneficial bacteria already present on the skin. By nourishing these microbes, prebiotics help maintain their growth and activity, which can have positive effects on skin health and appearance. Finally, postbiotics refer to the byproducts of probiotic fermentation. These substances, which include peptides, enzymes, organic acids, and antioxidants, can have beneficial effects on the skin. They help to strengthen the skin barrier, promote skin cell turnover, reduce inflammation, and provide antioxidant properties. By incorporating cosmeceuticals with probiotics, prebiotics, or postbiotics into skincare routines, individuals can potentially support the development of a healthy and balanced skin microbiota. These products aim to optimize the skin's natural defense mechanisms, enhance its resilience against environmental stressors like pollution, and contribute to overall skin health and aesthetics.
Additionally, building a healthy body from the inside out is also crucial for the well-being of the skin microbiota and overall human health. The condition of our skin is often a reflection of our internal health and various factors such as nutrition, hydration, lifestyles choices and overall wellness can significantly impact the balance and functions of the skin microbiota. Please note that maintaining a balanced and nutritious diet rich in vitamins, minerals, antioxidants and essential fatty acids can support the health of skin microbiota. Adequate hydration is also essential for proper skin function and microbial balance. Additionally, regular exercise, stress management and sufficient sleep contribute to overall well-being, which can indirectly influence the skin microbiota.
3/ Active ingredients available in the cosmetic market
In this section, I will introduce some active ingredients available in the cosmetic market that are known for protecting human skin against air pollutants and also the application of metagenomics to examine how the skin microbiota changes after application of active-containing products.
To protect our skin against toxically external factors, pollution in this case I will introduce you to a couple of active ingredients from CLARIANT.
EOSIDIN helps to protect skin against indoor pollution.
Indoor pollution is a significant concern as homes are heavily polluted, with roughly 2 to 5 times more contaminants than outdoors. Sources include household products, tobacco smoke, dust, heavy metals, and particulate matter. This pollution directly affects our health, well-being, and skin quality, leading to problems like itching, irritation, dryness, allergies, and hypersensitivity.
Eosidin is a natural active ingredient extracted from green citrus unshiu, which originates from Jeju Island, Korea. It is enriched with high concentrations of synephrine and hesperidin. This ingredient is specifically formulated to target indoor pollution and regulate skin immunomodulation, effectively preventing atopic-prone skin conditions and hypersensitivity. Eosidin's key feature is its ability to block the JAK/STAT6 pathway, thereby reducing eotaxin synthesis and histamine release. Consequently, it aids in reducing skin sensitivity and maintaining a healthy skin barrier.
REDSNOW helps to protect against air pollution.
With a high speed of industrialization, air pollution has become an alerting issue that has negative impacts on human health in general. When it comes to skin, air pollution causes wrinkles, irritation, premature aging, and so on. This ingredient can reduce the production of Reactive Oxygen Specices (ROS) by blocking the aryl hydrocarbon receptors (AhR) and also NADPH oxidase (NOX) activation pathway.
Redsnow is the natural active ingredient that is derived from Camellia japonica flower from Jeju island, Korea. It is enriched with high concentration of protocatechuic acid, a phenolic acid with powerful antioxidant and anti-irritation activities.
For more information about active ingredients that have ability of protecting skin against pollutions from CLARIANT, follows this link: https://www.clariant.com/en/Business-Units/Care-Chemicals/Personal-Care/Actives-and-Natural-Origins/Active-Ingredients/Natural-Actives/Environment-Protection
In addition to that, let me introduce you to an active ingredient that aids in rebalancing the skin microbiota. Through the application of metagenomics, the effects of products containing this active ingredient on the skin microbiota can be examined, providing insights into how it influences microbial changes.
That is ACTIBIOME from CODIF (France):
Actibiome is an active formulation composed of a carefully balanced combination of brown algae extract, green microalgae extract, marine exopolysaccharide solution, and earth marine water. This formulation has been specifically designed to strengthen and rebalance the skin's microbiota, resulting in a healthier and more homogeneous complexion. By utilizing Actibiome, the skin's microbial community is restored to a state of equilibrium, promoting overall skin health and a more balanced appearance.
Here are the positive changes observed in the skin microbiota after one week of treatment with Actibiome as recorded in one study conducted by Codif. During periods of stress, harmful bacteria tend to thrive while beneficial bacteria decrease because stress can trigger various physiological and hormonal changes in the body. However, after one week of treatment, a balance is restored, and the diversity and abundance of the microbial community resemble the initial conditions more closely.
In conclusion, maintaining a healthy and balanced skin microbiota is crucial for optimal skin health. “Omics” including metagenomics and metabolomics in this research serves as a valuable tool for analyzing the skin microbiome and understanding the impact of various factors on our skin. This knowledge allows us to develop effective strategies to restore and rebalance the skin microbiota. Additionally, there are numerous products available in the form of probiotics, prebiotics, and postbiotics that aim to enhance the health of our skin microbiota. By utilizing these resources, we can support and promote a healthier skin microbiome.
Chloe
Cosmetics x Science
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