Skin is exposed to harsh external stressors every day, which can have an impact on our delicate skin microbiome. With many skin conditions now linked to imbalances in skin microbiome composition, there is an obvious need to understand how to treat such imbalances – as well as a need to identify potential stressors, and when and how to protect our skin.
For this Quarterly Review, we have taken a look at some of the latest research addressing emerging technologies and treatments for the protection of the skin microbiome, as well as the vulnerability (or potential resilience!) of our microbes…
Clinical treatments and trials for skin microbiome imbalances
Many common skin disorders – such as atopic dermatitis, acne and psoriasis – have been associated with an imbalance in the skin microbiome, known as a ‘dysbiosis’. The hypothesis that such loss of microbial balance could be restored via microbiome manipulation strategies has opened exciting new paths for both the dermatological and cosmetic fields, and a new paper  has now provided an overview outlining the most promising approaches for the treatment of various skin conditions:
Skin microbiome transplantation was oneof the first microbiome manipulation strategies to emerge – following the better-known fecal microbiota transplantation (FMT) method, which is used for the treatment of gastric Clostridium difficile infections. When it comes to the skin, a microbiome transplant refers to the transfer of the skin microbiome of a healthy individual to the washed or disinfected skin of another person carrying a specific skin disorder to improve their skin condition.
Skin bacteriotherapy involves the placement of pure cultures with health-promoting properties onto the disinfected skin of a person with a specific skin disorder, in the form of a topical product. Such products may contain a whole range of microbiome-boosting ingredients, such as probiotics (living bacteria), postbiotics (tyndallized bacteria or bacterial cell lysates), purified enzymes or fermentation products or supernatants (read here for a breakdown of pre-, pro- and post-biotic skincare ingredients).
Prebiotic stimulation refers to the addition of prebiotics – ingredients with a bio-selective activity that exerts a beneﬁcial effect on the host and attempts to improve the host’s health – to the skin as a supplement to stimulate the growth of speciﬁc health-promoting microbes.
The researchers provide examples of different clinical studies performed throughout the years – such as the use skin microbiome modulation to treat acne vulgaris and microbial transplants to treat body odor – and highlight some of the promising scientific data now available to support such approaches.
Despite challenges and hurdles to overcome, the review indicates a bright future laid ahead for skin microbiome modulation in the treatment of skin conditions. The ﬁrst available study outcomes are already very promising, and much more data are expected from ongoing clinical trials in the near future.
Outside of the clinic, a series of recent papers have been looking into whether every-day products such as cosmetics or textiles used for clothing can impact our skin microbiome, and what can be done to help…
As the importance of the skin microbiota is increasingly acknowledged, a concern that is often raised is whether certain ingredients present in cosmetic products – such as preservatives – have a negative impact on the skin microbiome.
Preservatives are essential to ensure that cosmetic formulations remain safe for use via control of microbial contamination. Whilst the activity of preservatives is clear, little information exists on the potential impact that common preservative systems, in full formulation, have on the skin’s resident microbiome.
A group of researchers have now presented an analysis  of four in vivo studies conducted using adult leg skin microbiome samples to examine the impact of different preservation systems in full formulation, in different products formats and with varying durations of application.
The results show that species-level taxonomic assessment revealed no statistical differences in community profile following product application. Focusing also on the assessment of skin biodiversity using indices such as Chao1 (richness) and Shannon (richness and abundance), the authors demonstrated that these elements are not impacted by the product use.
This work demonstrates that despite the antimicrobial efficacy of the preservatives in vitro, the skin microbiome is not particularly impacted by preservative containing products in vivo. Although it has been shown that the leg skin microbiome is not perturbed to a point where it is unable to recover to its baseline state following product use, additional analysis may be needed to assess the short-term impact of product application.
Over the past few years, the initial focus of microbiome research within skincare has been on the interaction of the microbiome with the skin, or the microbiome with cosmetic products. Clothing as part of the microbiome trend played a subordinate role when the spotlight came to deodorant, but a new publication  has now put clothing and fashion industry – a multibillion market with fast-paced innovation – centre stage.
Providing an overview of the state of research within this area, the authors outline how the nature of antimicrobial finishing in textiles can disrupt the skin microbiome, and the benefits of more natural and microbiome-friendly textiles to combat challenges such as textile odors, as well as skin conditions and infections.
In the years 1990 to 2000, for example, laundering habits shifted from chemical-based detergents and hot washes towards enzyme-based detergents and cold washes, driven by environmental and economic reasons. However, metabolite load can increase in the fibers over time as more sweat and sebum secretions are transferred to the clothes and are not sufficiently removed by the laundering process. Specifically, hydrophobic molecules such as apocrine and sebaceous secretions can adhere and bind to clothes, leading to a build-up of metabolite precursors.
This might be an important explanation for permastink (the unpleasant smell that won’t wash out of textiles), and antimicrobial textiles with odor-resistant properties are now becoming a requirement on the market. Outlined within the new publication are various methods being explored to address this demand such as the use of seaweed or bamboo fiber, which has been suggested to contain a unique antibacterial bio-agent.
Research exploring the impact of the textile microbiome on the skin and has also identified the direct involvement of particular microbes on factors such as skin moisture content or malodor development, with investigations into so-called ‘microbiome-smart’ textiles making use of good microbes, or their enzymatic potential.
Also highlighted is emerging work investigating probiotic bacteria as an alternative for typical biocides and antimicrobials to reduce current toxicity and resistance problems. However, challenges remain. If probiotics are used, for example, it is important to ensure that the bacteria stay alive on the substrate as the viability of the bacteria affects the efficiency of the product.
Masks in the COVID-19 era
Staying on the topic of textiles, ‘maskne’ is a new threat to our skin microbiome that has emerged during the COVID-19 pandemic (read more about maskne here). A recent review  has addressed the impact of fabric-mask-wearing on the skin microbiome and dermatological conditions, as well as the therapeutic role of biofunctional textiles in improving the skin microenvironment.
As explained within the review paper, the disruption of the healthy skin microbiome associated with mask-wearing has profound implications on several dermatological conditions such as eczema, acne and perioral dermatitis, with bacterial dysbiosis implicated in its pathogenesis. The new moist warm microenvironment and textile–skin friction created by mask-wearing increases the susceptibility of skin to irritation, dermatological skin disorders linked to microbiome dysbiosis and skin barrier impairment.
The authors also provide some therapeutic considerations useful to prevent skin inflammation and maskne under occlusion. As well as biofunctional textiles, these range from day-to-day routines such as cleansing, leave-on skincare and moisturizers, as well as topical treatments such as active ingredients and formulations for acne.
So, how worried should we be about the fragility of the microbiome? Well, the good news is that results of a study running over two years suggest our skin microbiome has indeed evolved some mechanisms of resilience…
Skin microbiome variation across time
As the skin microbiome is still a relatively young research area, data from long-term studies are not yet the rule. New research , however, provides one of the first exceptions here, as it evaluates data from a study that has now been running for 2 years.
It is now well evidenced that the human skin microbiome is highly personalized, depending on, for example, body site, age, gender and lifestyle factors. The temporal stability of an individual’s skin microbiome – its resiliency and robustness over months and years – is also a personalized feature of the microbiome, and data from the new study can now also confirm this.
Across a population of 115 healthy adult men and women, facial skin microbiome composition and diversity were studied at regular intervals over 2 years and were observed to be relatively stable, showing only minor variation on average throughout the study period. However, for some individual subjects, composition, diversity and relative abundance of specific organisms showed substantial changes from one year to the next, and these changes were associated with changes in stratum corneum barrier function and follicular porphyrins.
The authors of the study conclude that the results from this 2-year longitudinal study add to our understanding around the stability of the facial skin microbiome. Despite some variation on the individual level, the results show that overall, even with the rigors of daily hygiene, UV exposure, human, and animal contact, the facial skin microbiome is amazingly robust.
With this new research in mind, it’s still essential to be wary of how we treat our skin and its microbiome.
As mentioned, the skin of some individuals is more sensitive than others, and in our fast-paced human world new stressors in the form of products or even changing environments can still pose a threat, and so ongoing research into the vulnerability and protection of our skin microbiome remains key.
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1 – Callewaert, C. et al. Skin microbiome transplantation and manipulation: current state of the art. Comp. Struct. Biotech. 19, 624–631 (2021).
2 – Murphyl, B. et al. In-vivo impact of common cosmetic preservative systems in full formulation on the skin microbiome. PLoS ONE 16, e0254172 (2021).
3 – Boradhead, R. et al. The future of functional clothing for an improved skin and textile microbiome relationship. Microorganisms 9, 1192 (2021).
4 – Teo, W.-L. The “Maskne” microbiome – pathophysiology and therapeutics. Int. J. Dermatol. 60, 799–809 (2021).
5 – Hillebrand, G. G. et al. Temporal variation of the facial skin microbiome: a 2-year longitudinal study in healthy adults. Plast. Reconstr. Surg. 147, 50S (2021).