50 SKIN MICROBIOME
Development of a colonised skin model
Dr Louise Suleman, Dr Samantha Thistleton - Perfectus Biomed Group, UK
Much of what we know about the skin’s microbiome has only been discovered in the past decade. It has long been known however, that human skin is home to a vast array of microorganisms, and they live there in huge numbers (a widely accepted estimate is a billion bacteria per square centimetre of skin). Perhaps because they largely live in harmony with us and cause no harm, the importance, complexity and impact of this ecosystem took a while longer to come to our attention. In 2007 the United States Institutes of Health established a research initiative called the Human Microbiome Project1 focusing on better understanding the role of microbial flora not just on the skin, but also in the gut, oral cavity, urogenital tract and nasal passages. The published findings from this ambitious project have undoubtedly fuelled a surge in interest around the skin microbiome which has filtered through to consumers. Understanding that the skin microbiome is unique to each individual has provided a new opportunity for manufacturers to engage consumers in the trend for the personalisation of skin care routines with products claiming to balance, protect, correct or enhance the skin microbiome. Opportunities may also arise for more customised treatments of common skin disorders such as acne, eczema and rosacea.
Microbiome vs. microbiota Before we continue, it is important to highlight the terminology used in this field. Many of the articles written, conferences held and products on the market refer to the ‘microbiome’, but there is another word, often used interchangeably; termed the ‘microbiota’. Technically ‘microbiome’ refers to the microorganisms and their genes, whereas ‘microbiota’ refers only to the types of microbes themselves. In this article we refer to the microbiome as meaning the entire population of bacteria, fungi, viruses and archaea resident on human skin.
The role of the microbiome Considered the body’s largest organ, with an average area of 1.8m2
, human skin plays a vital
role in supporting our overall health. Not only is skin a physical barrier protecting bones, organs and preventing the invasion of foreign pathogens, it also plays a key role in physiological regulation and sensation. Despite the harsh landscape of skin, particularly the desiccated, nutrient-poor and acidic environment (factors that can limit skin’s vulnerability to opportunistic pathogens) a diverse range of billions of microorganisms makes it their home – this is our microbiome.2 The significance of a ‘healthy’ skin microbiome
becomes apparent when we consider that not all of the microorganisms that inhabit the skin microbiome are commensal (non-
1x10∧8 CFU mL-1■ 1x10∧
6.00 5.00 4.00 3.00 2.00 1.00
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pathogenic permanent residents) or transient (temporary residents), some will be pathogenic potentially causing disease. It is also possible that even commensal microbes can exhibit pathogenic potential under certain conditions. Examples include Staphylococcus aureus, Propionibacterium acnes, and Malassezia spp., well known skin commensals that are also implicated in a range of skin disorders such as atopic dermatitis, acne, dandruff and psoriasis. It is understood that microbial dysbiosis (or microbial imbalance), host genetic variation, and immune status may drive the transition from commensal to pathogen.3
In research carried out
by Kong et al. it was observed that skin bacterial diversity decreased during the flare stage of atopic dermatitis (compared to healthy, age- matched controls) parallel with increased relative abundance of S. aureus, but increased during the post flare status, which indicated a link between disease severity and microbial diversity.4
Skin care and the microbiome Diversity, density and the balance of species within the microbiome appears to be important in maintaining healthy skin. Therefore, it is not surprising that ‘caring for your microbiome’ has become the preserve of the skin care market. There exists a growing trend for cleansing routines to be far less astringent and ‘stripping’ than in the past. There is a notion that we should in fact ‘feed’ our skin. Many products have been launched that largely promote the health and abundance of bacteria that your skin needs by way of including prebiotics, probiotics and postbiotics. This is paralleled with the huge rise in personalised beauty and personal care based on individuals own skin type, lifestyle and environment. With every opportunity comes a challenge;
not only is the skin microbiome unique to each individual it also changes with age, external factors such as climate, UV exposure and particulates in the air. Furthermore, it even varies across the surface of your skin between different sites on the body. Microbial profiles have been shown to differ in the type of microorganisms and the proportion of those species between dry oily and moisture-rich sites of the body. It is also expected that skin pH, skin conditions and individual skin care routines may also impact a person’s microbiome. But without costly and time- consuming analysis no one knows exactly what makes up their microbiome and what influences
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