Lab Notes

What is the Skin Barrier and why does it matter?

The term "Barrier" is now plastered all over the skincare industry. It has become the new buzzword in marketing. However, not everyone knows its meaning.

You’re probably hearing about barrier repair a lot these days. While the concept has been around a long time, it’s only relatively recently that consumers are becoming more educated about the importance of the skin barrier to overall skin health. Unfortunately, that education is not always based in the facts. So, as always, we’re taking the evidence-based approach to helping you understand more about what the skin barrier really is, what it does, and why skin barrier health should be important to you.

So what is the skin barrier? Is it the same as the moisture barrier?

The terms skin barrier and moisture barrier are thrown around a lot these days. They’re often used interchangeably, yet the terms describe distinct functions of the skin. In this intro guide, we'll explain what these two barriers are, how they're different, and how you can support each one's important work in protecting your skin.⁠

The Skin Barrier

The skin barrier is simply the broadest definition of skin functions: a barrier to the outside world. It keeps the “good” in (moisture, bodily fluids, and of course your organs) and the bad out (everything from dirt, pollution, viruses and other pathogens, to damage from things like radiation!). Preventing moisture loss via the moisture barrier is a critical function of the skin barrier, it’s just one of its many functions, other key “barriers” are: antimicrobial, antioxidant, immune response, and photoprotection.

The Moisture Barrier

The moisture barrier is not a region in the skin, nor a specific structure. It’s actually a dynamic system that provides a hydrophobic (water-repelling) barrier, preventing the entry and escape of most hydrophilic (water-loving) or charged molecules.


Why is the Skin Barrier important for skincare?⁠

Evidence is gathering that many skin issues, once thought to have independent causes and solutions, are in fact rooted in skin barrier health. In other words, for many conditions, we have been treating the symptoms and not the cause. For example, take Atopic Dermatitis (also called atopic eczema), a rather common skin condition associated with inflammation, itchiness, and other unpleasant symptoms. An emerging view of Atopic Dermatitis (also called the “outside-in theory”) proposes that it starts with a weakened permeability barrier which in turn ignites a spiral of exaggerated inflammatory response. In other words, a weakened barrier causes inflammation and itchiness, and those symptoms further damage the barrier, making the problem worse, and so on.

There is very promising research here, and we are closely paying attention to this emerging view. Fun fact: there is even research showing that supporting an infant's moisture barrier in the first three months may decrease food allergies later in life. The science is still young, but based on the quality of these studies, it looks promising.⁠

How does the Moisture Barrier work?

We believe that it’s essential to know each component of the barrier to better understand how barrier repair works and how to support it.

Acid Mantle⁠

Ever wonder how the skin “knows” when to heal itself? When to grow new cells or shed old ones? The graduated pH in the stratum corneum is one of the determinants of skin processes, including when to start barrier repair. All of these processes and more are dictated by pH as it is a very sensitive indicator of the skin cells' environment.

Tight Junctions and Desmosomes⁠⠀

Tight Junctions and Desmosomes are the main structures that hold your skin cells together. When your skin gets exposed to UV, the TJs in your Stratum Granulosum are deactivated. They lose hold of the adjacent cells, which leads to peeling and increased water loss (this is more commonly known as a sunburn). Desmosomes, on the other hand, dictate the cohesiveness of your uppermost layers of the skin. If you have dry skin, the desmosomes are not properly degraded, so they hold on to the skin's uppermost layer as much as possible. This leads to the visual appearance of rough and flaky skin.⁠⠀


Aquaporins are water channels in the skin that dictate how the lower layers of your skin get hydrated. They have some very interesting properties, for example, when glycerin gets transported through an Aquaporin 3 channel, the aquaporin signals your skin to produce more Ceramides, Cholesterol and Fatty acids. This eventually leads to a healthier moisture barrier. ⁠⠀⁠

Serine Proteases⁠

Serine Proteases regulate many processes in the skin. An excess of them in the skin leads to inflammation, barrier damage, and pigmentation. For example, conditions like Rosacea and Atopic Dermatitis lead to an increase in Serine Proteases that in kickstart a cycle that ends in the two skin diseases' unpleasant and often painful symptoms. ⁠⠀

Other components of the moisture barrier

The above three components are some of the most important to understanding the moisture barrier. Other key components include:

  • Lamellar bodies, which continuously repair the barrier lipids⁠
  • Barrier Lipids including Ceramides, Cholesterol and Fatty acids⁠
  • Keratinocytes and their cornified envelope, which enables them to resist damage⁠
  • Natural Moisturizing Factors that keep your keratinocytes hydrated⁠ (and thus functional)
  • Water Gradient, dictates a lot of processes such as desquamation and Filaggrin degradation⁠
  • Calcium Gradient, dictates Barrier Lipid production and other processes⁠
  • Pro-inflammatory cytokines that affect barrier lipid status⁠

The Permeability Barrier

The Moisture Barrier is the best known component of the Skin Barrier, but another important component to overall skin health is the permeability barrier, which is associated with many common skin issues.

There are three major components of the Permeability Barrier. Although other components of the permeability barrier play significant roles, injury to these three is much more commonly associated with skin issues:⁠⠀

1. “The Lipid Threesome⁠”

Ceramides, Cholesterol, and Fatty acids make up the majority of the barrier lipids. (Side note: barrier lipids=intercellular lipids=cement lipids=lamellar layer lipids) Ceramides make up 50% of the barrier lipids, while Cholesterol accounts for 25%, and 15% are from Fatty acids. Ceramides are of different classes, and each plays a significant role in the structure of the barrier. Cholesterol maintains the fluidity of the structure to avoid tearing during skin stretching. Fatty acids have different lengths and functions in the skin. These three components form very organized layers between cells, which prevent the entry and escape of molecules. ⁠⠀

2. The Bouncer⁠⠀

Corneocytes are the mature keratinocytes on the outermost layer of the skin. As the keratinocytes (skin cells) differentiate towards the skin surface, they start forming a cornified envelope, surrounded by involucrin proteins. These proteins attach themselves to the barrier lipids, adding extra hydrophobicity and protection. Corneocytes are also linked by Corneodesmosomes, which hold the cells together as they move outward. ⁠⠀

3. The Moisture bombs⁠⠀

Corneocytes have built-in inert hydration bombs (Filaggrin) inside them. When cells detect low water activity in the upper layers, they detonate these bombs, which degrade into NMFs that hold water to maintain hydration. Interestingly, overhydrating the skin prevents the detonation of Filaggrin. Which makes sense; why would your skin waste precious resources if you will provide it anyway? Another reason why adding too much water to the skin is not helpful. ⁠⠀

The “Other” Skin Barriers

This is just an introduction to some of the key components and functions of the skin barrier. There is lots more to unpack, lots more coming soon!

By the way: We discuss all these concepts on Instagram, and sign up to our newsletter below to get skin science updates right in your inbox.