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The Barrier Layer is Elemental to a Healthy Skin Microbiome

Understanding the Skin Microbiome: The Key to Healthy Skin | Marie Veronique


"Le microbe n’est rien, le terrain est tout."
- Louis Pasteur

As everyone has heard by now the skin is our largest organ, measuring in at 1.8 square meters and supporting an astonishingly wide variety of habitats. It also is home to approximately one trillion microorganisms of about a thousand different species, including bacteria, fungi, viruses, and even mites (Demodex).

The skin microbiome is often compared to the gut microbiome, though upon closer inspection the comparisons don’t quite run in parallel. The major dissimilarity is that unlike the gut, which offers an almost ideal environment for the growth of fermentative bacteria, the skin is vast expanse of inhospitable territory. Much of it can be likened to the Great Salt Lakes area; dry, salty, acidic and nutrient poor. Think elbows, knees, legs and arms for example. However, what stands out on the skin map, with its variety of distinct ecosystems resulting from conditions which favor different subsets of organisms, is the populous nature of the facial area. It’s like looking at an urban center surrounded by swathes of countryside dotted here and there with small towns. The urban area is clearly the cool place to be; it is thriving with different species of microbes, fungi and mites; lipophilic microbes such as Cutibacterium acnes spp, fungi like Malassezia spp, as well as the Demodex mite in the hair follicles of the eyelashes. On a side note, the Demodex mite is known for its vigorous, some might even say debauched, night life — next time you go dancing at a crowded club it would be fun to imagine that you’re a Human Demodex who’s ventured out of your hair follicle for a night on the town. In any case the facial area, and to some extent parts of the back, are the regions where we can expect to see different species of microorganisms thriving and in abundance, sometimes beyond what we might like; for example if you’re a teenager dealing with breakouts you most likely have an overcolonization of a strain of Cutibacterium acnes that can cause acne.

The good news is that most of the microorganisms inhabiting these regions are commensal, i.e. harmless, while those that are symbiotic, like Staphylococcus epidermidiswhich keeps pathogens like Staphylococcus aureus in check, are working tirelessly to keep you healthy. Even the human Demodex mite is just a nuisance to most people, though it is associated with rosacea in folks where the mites tend to get out of hand—with rosaceans playing host to about fifty per cent more Demodex than non-afflicted people.

We are leaning more about the skin microbiome every day but it’s a relatively new field of investigation compared to that of the gut microbiome, which explains why, to date, much more has been written about the gut microbiome, with the skin running far behind in second place. In lieu of studies directly involving the skin microbiome some researchers have made assumptions based on gut research and applied them to the skin microbiome as it contributes to skin function. Rather than taking that approach I suggest it would be more helpful to examine the skin microbiome in its own right, starting with a few basic facts.

The Origins + Function of The Skin Microbiome

The residents of a skin microbiome start forming, it’s called “seeding,” at birth of the host. These original colonists help to train the immune system, which learns to differentiate between commensal organisms (those with a neutral or beneficial impact on their host) and pathogens which want to take over. At puberty the final stage of microbiome development for an individual is reached. This is the microbiome you will carry with you into adulthood, subject to major changes in geographical location.

The skin microbiome’s main task is to protect the skin from pathogenic invasion. It does so by via an ingenious communication system. Microbes collaborate with the human immune system via “crosstalk” that goes on between the microbiome and its human host. The human immune system continuously scans the microbiome for information about metabolic state and colonization, and the microbes reply by secreting metabolites. This ongoing communication results in, among other things, the release of antimicrobial peptides to battle invaders, or an upswing in the creation of the bacteria-derived short-chain fatty acids that influence human epigenomic pathways.

The Terrain is Indeed a Major Player 

The terrain matters a great deal certainly, as we see in the example of facial skin with its lipid-rich territories where microbes thrive. Different species and different strains can be found in the lipid-rich areas around the hair follicles because conditions are favorable to their growth. For example, C. acnes,a common microbiome resident, feeds on the sebum which someone in the middle of puberty will be producing in excess.

But it turns out acne is a little more complicated than a simple cause and effect chain of events—be a teenager, produce more sebum, attract more C. acnes, the result is acne. In fact, there are different strains of C. acnes--some strains can produce metabolites that deter infection by pathogens, while other strains have a causative role in the development of acne. One strain is commensal or mutualistic, while another strain is pathogenic. (1) (S. Fitz-Gibbon et al. J. Invest. Dermatol. 133, 2152–2160; 2013).

Circling back to Pasteur’s observation, the latest research indicates that while the terrain is crucially important, the particular microbe matters too. In order to ascertain their impact on the skin we need to examine existing, residential microbes at the strain level.

Diversity – Is It Important?

The desirability of diversity with respect to the skin microbiome is in the present era rather an old-school position: “a healthy skin is a reflection of a balanced, widely diverse microbiome, skin disorders like atopic dermatitis reflect underlying problems with epidermal barrier impairment and disturbances in the skin microbiome.” (2) Microbiome in Atopic Dermatitis, Uwe Wallina, Clinical, Cosmetic and Investigational Dermatology)

Actually no, at least to the “widely diverse” part, a healthy skin can host only a few resident species and still be perfectly healthy. It’s not a question of diversity, but rather 1) which strains are present and 2) establishing a sufficiencyof residential bacteria such as S. epidermidis and the commensal strains of C. acnes, crucial to maintaining lipid regulation as well as barrier resilience and integrity.

We can use atopic dermatitis or eczema to illustrate these points. Atopic dermatitis (AD) or inflammation of the skin, affects ~10–20% of the general population at present, and that number is increasing, especially among children (“Incidence of AD has increased 2- to 3-fold in industrialized nations, impacting approximately 15% to 20% of children and 1% to 3% of adults worldwide.” (3) (Overview of Atopic Dermatitis, Carmela Avena-Woods)

When it comes to specific bacterial involvement, researchers have ascertained that in ~90% of AD patients the skin becomes colonized by Staphylococcus aureus, of which 50% are toxin producing. The toxins, Staphylococci exoproteins and superantigens, activate the host inflammasomes, evoking inflammatory reactions. As S. aureusmultiplies so does its cousin, Staphylococcus epidermidis, a “good” or symbiotic microbe that produces antimicrobial peptides and bacteriocins in response to invading pathogens. (4) (Iwase T, Uehara Y, Shinji H, et al. Staphylococcus epidermidis Esp inhibits Staphylococcus aureus biofilm formation and nasal colonization. Nature. 2010;465(7296):346–349.)

While different problems related to barrier dysfunction are certainly causative agents, eczematic flares also in all likelihood indicate an overabundance of S aureus. This suggests a corresponding lack of S epidermidis to control pathogenic growth. But this is specific mutualistic microbe vs pathogenic microbe action that won’t be addressed by introducing more diverse species. Rather what is needed here is an increase in an existing residential microbe, S epidermidis, with its AMP power.

Another Layer to The Skin Story — The Epigenetics of It All

We’ve identified the terrain and the inhabitants of the microbiome at the strain level as being important components in maintaining skin health. Of equal importance is the role we tool – using humans play. We are always tinkering with the environment, whether it’s the one under our feet or the ecosystems we are host to. We can’t seem to help ourselves; whether it’s as simple as cleansing the skin or something as life-threatening (at least for the microbes who are targeted) as benzoyl peroxide treatments or dermabrasion.

It’s only natural; the face is what the world sees of us, so there’s a huge impetus to “improve” facial skin; make it smoother, clearer, more inviting to touch. What we fail to see is the smaller picture, namely that our actions have an impact on microbial populations within the skin microbiome, and actions detrimental to the skin microbiome can end up having undesirable consequences when it comes to our skin health overall. From the microbes’ point of view this is probably a given. Our repeated failures to understand even this very simple exercise in logic must make them want to scream with frustration.

How to Keep Your Commensal Microbes from Screaming, or, A Guide to Achieving Healthy Skin

A microbiome in balance certainly aids in the quest to improve barrier function, which is the sine qua nonof healthy skin. There are some things you can do in the aid of both.

Not surprisingly, adequate barrier function aided by robust commensal populations depend on such external factors as hygiene, topical treatments and skin care products. If you already suffer from some type of dermatitis, and there are growing numbers of you, here are some things to avoid as well as some things to add to your skin care routine.


To Avoid

  1. Over cleansing can be worse than no cleansing. Anti-bacterial soaps disrupt microbial balance, and over-exfoliation weakens the barrier layer, leaving skin vulnerable to pathogenic assault.
  2. Essential oils are volatile organic compounds with antiseptic properties that can be deleterious to commensal populations. There is also a high risk of irritation and allergic reactions associated with them, leading to some level of barrier dysfunction.
  3. Microcidal preservative systems kill indiscriminately, commensals as well as pathogens, and in so doing disrupt microbial balance of the skin. Even microcidal preservatives regarded as ‘natural’ and ‘non-toxic’ like phenoxyethanol and phenethyl alcohol are associated with a high incidence of skin irritation.


To Embrace

  1. Cleanse and exfoliate with pro-bacterial options like yoghurt. To cleanse, smooth about ¼ tsp full-fat yoghurt over face and rinse. To exfoliate, smooth about ¼ tsp over face and leave on 15-30 minutes, then rinse.
  2. Microstatic preservatives (where colonies don’t increase in size) like leuconostoc radish root ferment may be doubly beneficial to the skin. The preservative activity of products like Leucidal™ Liquid, approved by ECOcert, comes from a peptide secreted from the process of fermenting radishes with Leuconostoc kimchii, a probiotic lactic acid bacteria (LAB). Recent studies suggest there are many skin health benefits to be derived from these tiny LAB creatures, including “antioxidative and antiaging properties.” (5) Health Benefits of Kimchi (Korean Fermented Vegetables) as a Probiotic Food, Park Kun-Young, et al, Journal of Medicinal Food)
  3. Improve skin barrier function with barrier enhancing topicals containing components of the barrier layer that are needed for good task performance, e.g. ceramides, amino acids, natural moisturizing factor and the like. The skin microbiome includes the top layer of the epidermis, the stratum corneum. May we recommend our Barrier Support Duo - a synergistic combination of two of our top-sellers including Barrier Restore Serum, which supplies nutrients that nourish and regulate barrier function, and Barrier Lipid Complex, which replenishes key lipids naturally found in the barrier.


Any topic discussed in this article is not intended as medical advice. If you have a medical concern, please check with your doctor.