Skin Microbiome 101

Oct 28th, 2024

Women during a treatment at the spa with microbes on her face

By Alex from Adobe Stock

Every skin care professional worth their salt understands the value of building and maintaining the strength and integrity of the skin barrier. I once heard an esthetician friend of mine put it like this, "Behind every skin condition and concern is a compromised skin barrier." I think most professionals would agree with that. However, amongst all this talk about improving the skin barrier, one very important piece is missing from the conversation: the skin microbiome. That’s right, we are talking about the collection of tiny living organisms mixing and mingling in the various ecosystems covering every square inch of our skin. Among these little living beings are bacteria, fungi and viruses that not only can influence our skin’s health but can directly impact every aspect of our skin and how it functions.

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Skin Structure

The skin barrier is often compared to a brick-and-mortar structure. The bricks are the skin cells made up of amino acids and other proteins, and the mortar is a lipid matrix made of 50% ceramides, 20% cholesterol and 10-15% fatty acids. This barrier effectively keeps pathogens, foreign bodies and external stimuli out of our body and ensures internal homeostasis throughout our body.

Woven into and sitting on top of this barrier is that collection of bacteria, fungi and viruses mentioned earlier- the skin microbiome. Approximately 1.5 trillion resident bacteria are on the skin at any given time, and roughly 1,000 different species. The most common species found on the skin are propionibacterium, corynebacteria and staphylococci. The ecology across the skin at different body sites varies, depending on the site.

The three most notable microenvironments are dry, oily and moist. Each of these microenvironments breeds different microbes. The skin microbiome is primarily made up of resident microbes. These microbes are more permanent in the skin and play a significant role in the overall health of an individual’s skin starting at birth. The resident microbes begin to colonize the skin immediately, even starting to form in the birth canal in the case of vaginal births.

There is another group of notable microbes as well that colonize the skin for a few hours to a few days. These microbes are picked up from the environment, the people we come in contact with, and other surroundings. These microbes are called transient microbes. Although transient microbes are not on the skin for long periods, they can trigger a shift in the balance of resident microbes.

This is part of the reason why our skin can react to changes in weather or climate. The skin microbiome directly impacts the skin barrier, as these two are intimately connected. If the skin microbiome is in homeostasis, the skin barrier is strong. If the skin microbiome is dysbiotic, the skin barrier begins to weaken, erode, and degrade leading to reactive, sensitize, and inflamed skin.

In a report by Hyun-Ji Lee, the shared goal of the skin barrier and skin microbiome is described. “Skin microbes do not simply reside on the skin but interact with the skin in a variety of ways, significantly affecting the skin barrier function. The skin microbiome and the skin barrier relate symbiotically to affect each other in physical, chemical, and immunological ways.”

Despite the different mechanisms of action, the skin barrier and skin microbiome have one shared goal- immunity. The skin microbiome controls much of our skin’s immune system, similar to how the gut microbiome controls the body’s immune system. When a threat is detected, the microbiome sends a series of signals to the body to launch an immune response. This response consists of AMPs, cytokines, and other inflammatory markers aimed at protecting the skin and ridding it of pathogens before the pathogens can enter the body. This immune activation presents as inflammation, sensitivity and other chronic inflammatory conditions like eczema, acne, psoriasis, and rosacea. The skin microbiome is really the first line of defense, even before the barrier, as this collection of living organisms is the arbiter of what our skin barrier reacts to and what it dismisses as passive.

Lee also adds, "The microbiome also stimulates a range of innate immune responses and maintains symbiotic relationships with the skin when the skin barrier is disturbed.”

When we have dysbiosis in the skin microbiome, the skin’s immune system becomes overactive eliciting reactions to external stimuli that should be considered benign. This is when we start to see red, reactive, sensitized, and inflamed skin and a complete erosion of the skin barrier.

In another report, it notes, “We recently observed that bacteria residing on the epidermis can be observed within the dermis of healthy normal human skin."

In an article in the Journal of Investigative Dermatology, it adds, "This surprising observation that bacteria can penetrate the epidermis illustrated how bacteria position themselves to directly influence immune responses.

The new term for this type of skin: leaky skin.

Leaky Skin

You may or may not have heard the new team leaky skin to describe this reactive, sensitized and inflamed skin.. Simply put, leaky skin is the term for a dysfunctional skin barrier triggered by skin microbiome dysbiosis. Studies show that if our skin microbiome is dysbiotic, it can physically degrade the skin barrier, eating away at essential lipids in the skin and eliciting inflammation along the way.

In a report by Hyun-Ji Lee and Miri Kim, it is noted, "Microbiome dysbiosis can cause damage to the skin barrier, which is associated with inflammatory skin diseases."

One of the most well-documented examples of this comes from the interaction between S. aureus and its effects on ceramide and filaggrin levels. Most of this data has been harvested from patients with atopic dermatitis, which is an inflammatory skin condition with strong ties to skin microbiome dysbiosis and skin barrier impairment.

In one report, it notes, “Strong associations have been shown between dysbiosis and the clinical phenotype of atopic dermatitis (AD).

Various studies have shown that S. aureus prompts skin to produce cytokines that degrade barrier integrity and enhance barrier degradation. The ability of staph aureus to penetrate the epidermis is also superior to other bacterial species, as shown in various tape-stripping experiments. Advanced S. aureus colonization is also found in cases of impaired filaggrin expression. Filaggrin is an important protein in the skin that binds keratin fibers in skin cells. Lack of filaggrin is another hallmark of atopic skin and linked to an abundance of s. aureus in the skin microbiome. Lack of filaggrin also enhances s. aureus’s ability to penetrate and cause further damage to the skin barrier.

Nakatsuji adds, “Studies show that S. aureus PSMα can stimulate keratinocytes to produce cytokines that promote skin damage and inflammation resembling AD.”

The Benefits of A Balanced Microbiome

A healthy, balanced skin microbiome benefits the skin's health in several ways. Most notably, a balanced skin microbiome will:

Prevent the overgrowth of pathogens, thus reducing toxin production and recruitment of immune cells.
Produce adequate protease enzymes to help turn over the stratum corneum
Produce adequate lipase enzymes to effectively breakdown and regenerate the lipid layer
Produce urease, free fatty acids, regulate sebum production and manage pH of the skin
Perform effective quorum sensing and biofilm production.
Drive antioxidant function and quenching of free radicals.

Ultimately a balanced skin microbiome will result in a more resilient skin barrier with a high tolerance for negative stimuli. The skin will appear stronger, function better, maintain barrier integrity and functioning, reduce fungal and bacterial overgrowths, and maintain sufficient water levels. A balanced skin microbiome reduces reactivity and sensitivity, along with reducing the appearance of various inflammatory conditions like acne, eczema, psoriasis, rosacea, etc.

Bottom line

The conversation around the skin barrier is a very important one to be having, and now we have one more giant piece of the puzzle. I’ve been speaking with many of estheticians, and it seems that sensitized skin is on the rise. I believe that this is in part because the skin microbiome is changing, the canvas of skin is changing, and treatments and techniques need to change with them.

The skin microbiome is a foundational piece of skin’s health, its role in skin health cannot be overstated. To achieve the best results for clients the skin microbiome must be addressed so we can continue to maintain and support a healthy, strong, and resilient skin barrier.