by Gopinathan K. Menon and Roger L. McMullen
November 22, 2021
The skin microbiome has been a hot topic for quite some time in skin research and for researchers. Both consumers and the cosmetic industry have boarded the bandwagon—sometimes with different end results in focus. There is a large and growing consumer base who believes that the skin microbiome is a rather delicate component of skin, which is ‘endangered’ by chemical and biological assaults from the ingredients (actives and preservatives) in personal care products. Proponents of this view tend to demand minimalist products that contain only microbiome friendly ingredients, or altogether shy away from multiple product use. Industry scientists have taken note, and have been working on microbiome-friendly product development, or using probiotic bacteria itself, their extracts, or their fermented products as active ingredients. A quick Google Scholar search on ‘skin microbiome and cosmetics effects’ turns up about 7,370 results, many of them published in less-known journals, but a significant fraction of them appear in better known, peer-reviewed journals.
The results and conclusions of many of these studies are as variable as the design of the experiments, duration of the studies, and investigative techniques employed. But the public discussions and internet chatter makes us wonder if we are skirting the issues of whether all topical products are bad for the microbiome, or whether it leads to changes of microbial ecology to a scale significant enough to change the physiology and health state of the skin. We raise the question about what deleterious effects of skin care products were noted, if any, before the microbiome-conscious era of skin biology research. Did product safety investigations reveal any serious concerns (which in hindsight may be due to microbiome dys-biosis) that caused the recall or discontinuation of typical moisturizing or anti-aging products? Could someone go back to an otherwise effective skin care product that was pulled out of the market for an unforeseen deleterious skin effect and re-test it for any effects it might have on the skin microbiome?
Wallen-Russell showed that: a) Higher biodiversity of microbiome equates to healthier skin; b) Changes in diversity, skin moisture, and TEWL (skin health parameters) appear to be caused in response to product use; and c) The more synthetic ingredients found in a product, the less of a positive effect on average biodiversity it appeared to have, especially within the first two weeks.1 This author concedes that the study should have addressed the lack of background information on the participants’ previous skincare regime, meaning the effects observed can be attributed to the use of other products by subjects before the initiation of this study. Finally, a longer-term study may be needed to give insight into the length of time an ecosystem, such as the skin microbiome, takes to readjust to a healthier, more natural state.
Obvious culprits that disturb the skin microbiome could be preservatives and anti-microbials. Yet, a very recent publication by Murphy et al.2 states: “An analysis of four in vivo studies that examine the impact of different preservation systems in full formulation, in different products formats, with varying durations of application demonstrated that despite the antimicrobial efficacy of the preservatives in vitro, the skin microbiome is not impacted by preservative containing products in vivo.” To us, these two studies exemplify reasons to re-evaluate the cosmetic-microbiome interaction with a different perspective. The human skin (and gut) microbiome has evolved along with our own evolution as a species; adapting to various skin care products that our species has used since the age of some of the earliest civilizations. In addition, microbes have an amazing ability to mutate and resist novel chemicals (natural and synthetic) that they encounter along the way. Thus, it could be rather naïve on our part to treat the microbiome as a fragile system, susceptible to change due to exposure to cosmetic products. While it is possible that a new chemical entity may adversely affect one or more of the microbial species in the short term, we could expect to see this ecosystem rebalancing itself—a kind of healing following its disruption.
As we well know, the visible effects of topically applied actives (drugs, cosmeceuticals, etc.) on skin appearance take longer than a couple of weeks to take effect. We should take into account that our epidermal cells are also able to adapt, degrade, metabolize, and detoxify various cosmetic/drug molecules; despite not having the capability for rapid mutations that enable adaptation and survival of our microbial commensals. There is also a vast literature on topical application of beneficial probiotics from the gut (or extracts of probiotics) and their fermentation products, which are known to modify the skin microbiome.
The skin microbiome is predominantly associated with demographic, lifestyle, and physiological factors, as well as chronological and environmental aging of the skin.3 In addition, it is also known that individuals in close-knit social groups (families or circles of friends) share similar profiles in skin microbial ecology. Global travel, migration, or long-term deployment to a different continent (such as with military personnel) could be expected to alter the skin microbiome to various degrees—mostly with little manifest changes in skin health and functions. Maybe the impact of such changes needs to be assessed scientifically before making blanket claims of negative or positive effects on skin health. By the same token, does prolonged social distancing, such as that experienced during the global pandemic, change the composition of our skin’s microbial ecology? These are areas that could be profitably investigated, and we hope that dispassionate and scientific discussions, rather than social media chatter, will form the basis of how we view our skin microbial ecology in the context of personal care.
References
1. C. Wallen-Russell, The role of every-day cosmetics in altering the skin microbiome: A study using biodiversity, Cosmetics, 6(1): 2 (2019); https://doi.org/10.3390/cosmetics6010002.
2. B. Murphy, M. Hoptroff, D. Arnold, R. Eccles, and S. Campbell-Lee, In-vivo impact of common cosmetic preservative systems in full formulation on the skin microbiome, PLoS ONE, 16(7): e0254172 (2021); https://doi.org/10.1371/journal.pone.0254172.
3. P.A. Dimitriu, B. Iker, K. Malik, H. Leung, W.W. Mohn, and G.G. Hillebrand, New insights into the intrinsic and extrinsic factors that shape the human skin microbiome, mBio, 10(4): e00839-19 (2019); https://doi.org/10.1128/mBio.00839-19.