Barrier Breakdown: The Basics of our Skin Barrier

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“Rome wasn't built in a day”

and neither was our skin barrier.?

Because good things take time to form, our skin needs at least 28 days to fully renew itself.?

In these 28 days, the barrier gives you your best face forward.?

So, slap on some barrier cream, grab your favorite drink and get ready for the lowdown on the skin barrier.

What is the Skin Barrier

Your skin’s barrier is generally thought of as the outermost layer of the skin, called the Stratum Corneum. It's basically the first line of defense against intruders like pollutants and toxins.

Components of the Skin Barrier

The skin barrier is composed of a variety of different complexes that all work together to ensure the barrier functions properly. In order to really understand this part of our skin we need to define exactly what these structures are.

Ready for the breakdown?

Corneocytes

Sometimes referred to as “dead skin cells,” Corneocytes were once live cells, called Keratinocytes, that got squished and died off. These flattened cells provide protection for the deeper layers of the skin.?

Made mainly of a protein called Keratin and its intermediates, which organize into tough bundles that provide strength and rigidity to the skin. This mechanical strength is necessary to fight against the tough environment.

Corneocytes also offer a safe space for water to hang out, helping to keep the top layers of the skin hydrated. Without water, enzymes that are crucial to the proper functioning of the skin barrier can’t function (more on this later).?

This tough layer of cells is sometimes referred to as the “bricks” of our skin barrier.?

Lipid Matrix

The oily substance that fills the gaps between the corneocytes, helping to keep water in the skin. The predominant lipids are cholesterol, ceramides and free fatty acids, collectively referred to as the “mortar."

These lipids organize into bilayer structures that are linked to the outer structure of the corneocytes. The more "water loving" heads of the lipid molecules line up while the more "oil loving" tails align forming layers.

The composition of the lipids and the structural organization play a role in how well the barrier functions to keep water in and invaders out.?

Cornified Envelope?

The envelope is a highly insoluble complex that engulfs the corneocytes, providing a tough barrier surrounding the cell. This membrane replaces what was once the plasma membrane found in Keratinocytes.?

It consists of linked proteins and bound lipids, notably ω-acylated-hydroxy-ceramides. This unique ceramide creates a starting point for the formation of the lipid bilayers.?

Corneodesmosomes

The main adhesive structures within the Stratum Corneum that hold the Corneocytes together. This adhesive prevents the Corneocytes from moving around, keeping the integrity of the barrier.

These protein structures are formed from a similar structure found in Keratinocytes called Desmosomes. These structures must be degraded for Corneocytes to shed off in the process called Desquamation (we will touch on this below).?

Natural Moisturizing Factors (NMF)

Water-attracting molecules that are formed from the breakdown of a protein called Filaggrin. These molecules are our skin’s natural humectants and are located within the Corneocytes. They help to keep water within the cell allowing for important processes to occur, preventing the cells from drying out, and helping to maintain the skin’s pH.?

These molecules include things like PCA, urea, lactic acid and free amino acids.?

How the Skin Barrier is Formed?

Cornification

Now that we have a better understanding of the key structures and components of the skin barrier, we can dive into the basics of how the barrier is formed.?

It all starts deeper in our Epidermis with the Keratinocytes. These cells gradually make a complex journey upwards through the Epidermis.?

Over their travels they start slowly changing in structure and production for certain lipids and proteins is ramped into high gear to create the materials needed for forming some of the components we defined above.

When the Keratinocytes have traveled as far as they can (they have reached the Stratum Granulosum), a few important things occur in order to be welcomed into the Stratum Corneum.?

High levels of calcium present in the Stratum Granulosum cause the release of profilaggrin, which is further processed into Filaggrin. The Filaggrin then facilitates the aggregation of the keratin fibers causing the collapse and flattening of the cell.?

The calcium also causes the rupture of a sack of lipids, coined lamellar bodies, that is produced when the Keratinocytes are still alive. This rupture releases key lipids and enzymes that are integrated into the Cornified Envelope and the lipid matrix. The enzymes break down the released lipids and transform them into the cholesterol, free fatty acids and ceramides.?

During this process the plasma membrane is replaced by the cornified envelope and the maturation to the final Corneodesmosome structure also occurs.?

And just like that, the Keratinocytes have found their new home within the skin.

Desquamation (AKA skin shedding)

Once the Keratinocytes have officially become Corneocytes the work isn’t over yet.?

The Corneocytes continue to migrate to the surface of the skin and eventually flake off through a process called desquamation (AKA skin cell shedding). This is the final destination.

(Okay but side note- does that scene with the log coming through the window in Final Destination live rent free anyone else's head?)

The process of skin cell shedding is thought to be a part of our skin’s physical innate immune system. Since cells are always being removed, any harmful microorganisms can go with it.

During this final migration more important stuff happens within the skin barrier.?

When the water activity is just right within the cells, our bestie filaggrin is broken down into our NMF. There are a few important molecules that form that I want you to know: trans-urocanic acid (UCA) and pyrrolidone-5-carboxylic acid (PCA). These two acids will become critical for maintaining the pH within the Stratum Corneum. Another cool feature about UCA is that it also has photoprotective effects against UV rays (the more you know guys!!).

Maintaining proper pH is critical for the processing and organization of the extracellular lipid matrix and for regulating enzymatic activity during this whole shedding event.

Alteration of the lipid matrix structure starts to reduce the cohesion between the cells. Then enzymes come in and start to eat away at the Corneodesmosomes. With the main adhesives weakened the cells reach their final destination (aka your clothes, the pillowcase, the floor... ok sorry if I grossed you out).

This marks the end of the journey for the cells that form our skin barrier.?

Techniques for Strengthening the Barrier

While I described a rather simplified version of how the skin barrier is formed, in reality there are a lot of different molecules involved that all have to be functioning properly in order to keep the integrity of the barrier.?Any kink in the processes related to barrier development and renewal could result in weakening.

Well, you may be thinking what causes these moving parts to stop working. It is a complicated answer but could be due to a number of reasons. The skin barrier is constantly being bombarded with environmental irritants. Combine that with changes related to aging, changes with the weather, different skin care products, lifestyle choices and your genetics- and our barrier might have a hard time running efficiently. Which can put you at risk for developing issues, like dryness, redness, rashes, sensitivity or even skin diseases like atopic dermatitis.?

So how can we support our barrier on a daily basis and ensure it stays strong??

Maintaining Water Levels

Maintaining proper water levels is a critical component in keeping your skin barrier strong. If you live in a dry environment, like I do, you will likely have to rely on skin care products to help boost this moisture.?

Glycerin, an often-undervalued ingredient, can be a huge help in pulling water to the Corneocytes. One of the neat things about glycerin is that it is able to be transported into the cell via a special water channel, called Aquaporin-3, that sucks it up like a straw.

Once we have the water in the cell we need to keep it there. This is generally where the lipid matrix comes in, but if you’d like a little help in this department, look for occlusive moisturizers. Occlusives act like “blankets” working to trap water in the skin. Examples of occlusives include things like petrolatum, lanolin and dimethicone.?

Supporting the Lipid Matrix

While utilizing occlusive moisturizers can be a good strategy for helping to increase hydration, supporting your skin’s natural lipids shouldn’t be ignored.?

While you certainly can find products that contain skin identical ceramides, cholesterol and fatty acids, there are also ingredients that can promote your skin’s natural ceramide production.?

If you are worried your barrier isn’t working the best it can- being gentle can go a long way.?Some products contain penetration enhancers whose purpose is to temporarily disrupt the skin barrier to allow for better absorption of active ingredients.?Laying off highly active formulations may give your skin barrier a chance to recover and strengthen overtime.?

Even some surfactants can cause barrier disruption.?Cream cleanser or cleansing balm products may be better cleanser choices as they tend to contain lower surfactant loads and more emollients.?

Lotions and creams that use “lamellar liquid crystal emulsifiers” form structures within the emulsion that mimic the lipid structures we see in our skin’s lipid matrix. This similarity is supposed to help reduce disruption once applied on the skin.?

Filaggrin

As we discussed earlier, Filaggrin is a key player in the formation of both the Corneocytes and our NMF. Some skincare ingredients on the market are able to increase the production of Filaggrin within the skin. This increase may help to provide structural support as well as an increase in the NMF.?

While it may be difficult as an everyday shopper to determine if an ingredient is helping with Filaggrin production, there are quite a few bacteria ferments on the market that have data for this.

Exfoliation

If your skin is not properly hydrated, enzymes required for desquamation may not be able to do their job in full. This causes a buildup of cells that never got released, leaving the skin feeling scaly, flaky and dull. Using gentle- I mean it be gentle- exfoliants on a regular basis can keep the shedding process moving along and aiding in skin radiance and smoothness.

Thanks for coming along for the barrier breakdown journey. As always, I hope you gained a deeper understanding for the complexities of our skin. Stay inspired!

Until next time friends!

References

[1] Dissecting the formation, structure and barrier function of the stratum corneum | International Immunology | Oxford Academic ( oup.com )

[2] Lipids and skin barrier function – a clinical perspective - Jungersted - 2008 - Contact Dermatitis - Wiley Online Library

[3] Dry skin, moisturization and corneodesmolysis - Harding - 2000 - International Journal of Cosmetic Science - Wiley Online Library

[4] The skin barrier in healthy and diseased state - ScienceDirect

[5] The Discovery and Function of Filaggrin - PMC ( nih.gov )

[6] Structure and Function of the Stratum Corneum Extracellular Matrix - PMC ( nih.gov )

[7] The mechanisms by which lipids coordinately regulate the formation of the protein and lipid domains of the stratum corneum - PMC ( nih.gov )

[8] Understanding the physical properties that affect the lipid organization in the skin barrier - Leiden University ( universiteitleiden.nl )