This skin care and dermatology landscape may be facing a fundamental shift due to a new philosophy of skincare. Dr. Ward talks us through how the relationship between the skin microbiome and skin barrier function are creating this change, focusing on harnessing the diversity of the skin microbiome like never before.
The skin microbiome is a very promising and exciting new area of dermatological and research focus. Until recently, the true potential and opportunity that a better understanding of the skin microbiome has been an unknown – but not for much longer.
In 2008, the National Institute of Health Common Fund launched an integrated ‘Human Microbiome Project’ to study the microbial diversity of five bodily sites to better understand the human skin microbiome. There is now extensive data on the human microbiome, providing insight into which organisms are resident, which are transient and, indeed, which might be affected by our attempts at intervention. 
We now know that, on average, a single square centimeter of human skin contains up to 1 million resident microorganisms. 
A stable microbiome-host interaction is essential to support skin health, immunity and skin barrier function. This is known as a commensual relationship as the skin benefits from hosting the microorganisms. Understanding the skin’s unique microbiome may answer still unrecognized functions of the skin related in particular to sensitivities and the effect of stress on skin. Both impact the stratum corneum (SC) barrier – the outermost layer of the skin.
“The skin is an intelligent
and dynamic organ.”
The skin microbiome and its role
An important role of the skin is to protect us from unwanted infiltration of toxins, radiation, pathogens and foreign organisms. The outer layer of the skin is largely responsible for this protection and any compromise in epidermal integrity will compromise the skin’s barrier function. In order to preserve barrier proper functionality, the skin’s unique microbiome balance needs to be maintained.
This balance, and the skin’s microbiome diversity, depends on many unique factors: age, sex, ethnicity, skin thickness, sebum level, genetic disposition, climate, and skin care routine. It is made up of millions of microorganisms (bacteria, viruses, fungi and mites), with bacteria and fungi often being seen as the most important inhabitants of the ecosystem.
Most of the bacteria that populate the skin fall into four different phyla categories: Actinobacteria, Firmicutes, Bacteroidetes and Proteobacteria. Gram negative bacteria are generally thought to be contaminants from the gut and not true skin commensals. There are also non-bacterial organisms living on the skin too such as demodex mites (often associated with rosacea) that feed on sebum and fungal species such as Malassezia.
Interestingly, infant skin (in utero) is sterile but the colonization process begins the moment of birth.
The skin barrier: physical and immunological
The skin provides a huge surface area for the largely harmless and often beneficial microorganisms. There is a symbiotic interaction between the skin (the host) and its microbiome. When this harmonious balance is disrupted, we are essentially disrupting the skin’s most vital function – that of defense.
The skin is constantly exposed to things that can disrupt the natural symbiosis between it and the bacteria it hosts. The commensal microbiome may be impacted by sun exposure, pollution, topical medications, specific molecules such as preservatives, antibiotics, pharmaceutics and even mechanical trauma or injury. It is this kind of barrier disruption that is thought to be responsible for, either in part or by exacerbating, inflammatory skin disorders such as acne, rosacea and eczema.
Any disruption to the skin’s barrier function can let in unwanted toxins, chemicals, irritants and foreign organisms, as well as letting hydration and micronutrients seep out. This is why preservation of the skin’s barrier function is absolutely critical to skin health.
“The concept is about working with
the skin rather than against.”
The skin is an immunological barrier too. The skin’s immune response is vital in healing wounds and infections, and also modulates the commensal microbiota that colonizes the skin. The skin is an intelligent and dynamic organ. It can discriminate between harmless commensal microorganisms and harmful pathogenic microorganisms that it might be exposed to, it is thought that this may involve the induction of immune tolerance.
Skin care and cosmetic trends
It is research in this area of skin microbiome biodiversity and immunity that has interested the cosmetic community, leading to the development of skincare that carefully targets the skin’s microbiome population.
“This new generation of skin formulations and skincare philosophy may fundamentally shift the cosmetics and dermatology landscape.”
A number of studies now suggest the benefit of repopulating the skin with Iive bacteria through probiotic based skincare. Some commercial skincare brands already exist that focus only on repopulating the skin’s microbiome. So, it may only be a matter of time before probiotics become generally accepted in skincare, much like they are in foods and supplements for optimizing gut health.
Soaps, cleansers, and hygiene products are all potential factors that contribute to the variation of skin microbiota. Since these products alter the conditions of the skin barrier, they therefore alter how the skin behaves. The idea with probiotic skincare is that it works in sophisticated harmony with the skin, supporting and recognizing its own diverse ecosystem and nourishing it. The concept is about working with the skin rather than against.
Supporters of probiotic skincare suggest that traditional and, in particular, dermatological regimes often work against the microorganisms with an anti-microbial approach. For instance, in the case of acne, traditional methods include daily cleansing, salicylic and glycolic exfoliators, retinoic acid and anti-microbials. The idea being to kill the harmful Propionibacterium Acnes bacteria. Critics say that this approach can cause long term collateral damage in the skin via skin barrier disruption and a reduction in micro-organism diversity.
New generation skin formulations incorporate probiotics and may include ingredients that can act as supportive agents for the skin’s diverse microorganisms. Ceramides are useful carbon and nitrogen sources for the bacteria, niacinamide helps culture bacteria and selenium rich thermal spring water also shows efficacy for helping support the micro-ecosystem.
This new generation of skin formulations and skincare philosophy may fundamentally shift the cosmetics and dermatology landscape. We may not have all the answers yet, but we can be sure that any development in the skin microbiome research will have a lasting impact on skin care and cosmetics trends.
 NIH 2008
 Hilary E Baldwin, Neal Bhatia et al. ’The Role of Cutaneous Microbiota Harmony in maintaining a Functional Skin Barrier’ Journal of Drugs in Dermatology 2017 16 (1); 12-18
 Borkowski AW, Gallo RL. The coordinated response of the physical and antimicrobial peptide barriers of the skin. J. Invest. Dermatol. 2011;131:285–287
 Mary Kober, Whitney Bowe. ‘The effect of probiotics on immune regulation, acne, and photoaging’ International Journal of Women’s Dermatology Volume 1 Issue 2 June 2015, Pages 85-89
 Journal of Drugs in Dermatology ‘The Role of Microbiota Harmony in Maintaining a Functional Skin Barrier’ Hilary E Baldwin, Neal Bhatia MD January 2017