Skin Barrier Science

Skin Barrier Science

Protecting your skin barrier is essential for maintaining healthy, hydrated skin all year round. However, winter conditions can be especially harsh on the skin's barrier. In this edition of Skin Secrets, Dr Sebagh explains what the skin barrier is, how to know if it is damaged and what to do to repair and protect this essential shield for your skin.

What is the skin barrier?

Your skin is made up of three main layers; the epidermis, the dermis and the subcutis. Each of these layers comprises a number of sublayers.

A diagram showing the skin barrier

Although the ‘skin barrier’ is typically thought to refer to the uppermost layer of the epidermis (the stratum corneum), in fact, the barrier function of the stratum corneum arises from the symbiosis of a variety of its components, which, together, regulate the movement of water through the skin and protect the skin from external aggressors.

The stratum corneum, also known as the horny layer, is made up of sub-layers of flattened, dead cells called corneocytes which shed regularly when the adhesive structures which hold the cells together (corneodesmosomes) degrade. This process is known as desquamation.

Depending on the location the stratum corneum typically ranges in thickness from 10 to 30 layers of these cells; the stratum corneum is thicker in areas like the soles of our feet and thinnest in our under-eye area (the most delicate skin on our body). 

What is the function of the skin barrier?

The 'skin barrier' is named after its function; it protects the skin from external aggressors including pollution, microbes, toxins, UV rays and crucially for this time of year, dehydration. It is also responsible for transporting vital nutrients to the rest of your skin. 

The pH of the protective acid mantle helps to protect the body from harmful alkaline chemicals as well as being an anti-microbial environment. The structure of the corneocyte layers which comprise the stratum corneum also contributes to the skin barrier’s ability to protect the body from bacteria and viruses. In particular, desquamation (the process by which the skin sheds regularly) prevents allergens and irritants from penetrating the skin.

Arguably, the most important function of the skin barrier is preventing dehydration. For this function, it is the lipid matrix that is crucial. Lipids are hydrophobic meaning that they do not mix with water. As such, the biochemistry of the lipid matrix creates a watertight seal preventing the loss of moisture from the inside out.

When the skin barrier becomes damaged it is unable to perform its crucial functions, leading to transepidermal water loss (TEWL), inflammation from invading microbes and external aggressors including free radicals.

healthy skin barrier vs damaged skin barrier

How do I know if my skin barrier is damaged?

The symptoms of a damaged skin barrier are often mistaken for conditions such as acne or rosacea. This is why it is crucial to distinguish between skin that is sensitive (i.e. prone to rosacea, eczema etc.) and simply skin that has been sensitised (caused by a damaged skin barrier). A great indication is if, after applying products in your skincare routine that are usually well-tolerated, your skin turns red, starts to sting or tingle then this may be a sign of a damaged skin barrier and sensitised skin.

Skin barrier damage can present itself in the following skin concerns:

    • Redness in lighter skin tones

    • Darkening of the skin for those with brown and black skin tones

    • Itching

    • Stinging

    • Tightness

    • Rashes

    • Increased breakouts

    • Dry Skin

damaged skin barrier signs and symptoms

Breakouts occur because when the skin barrier is compromised and TEWL increases, the skin attempts to compensate by triggering the sebaceous glands to produce more sebum. However, too much sebum can cause pores to swell, trapping bacteria and dead skin cells resulting in an inflammatory response that results in comedones and pimples.

Another sign of skin barrier damage is the presence of rough skin on your face and flaky skin on your body. This is what is typically known as ‘dry skin’ and it occurs due to a disruption of the process of desquamation. Typically desquamation takes 28 to 45 days in your thirties, 45 to 60 days in your forties and can take as long as 90 days in your fifties. However, when desquamation is delayed, corneocytes accumulate on the surface of the skin leading to rough or flaky patches of skin.

What Causes a damaged skin barrier?

At a cellular level the symptoms of a disrupted skin barrier can be caused by numerous triggers, both intrinsic and extrinsic.

Intrinsic Factors

Intrinsic factors affect the enzyme balance of the skin, the level of NMFs and a reduction in the water content of the stratum corneum. These chemical changes affect the breakdown of the corneodesmosomes that bind corneocytes together. When corneocytes do not go through the typical enzyme-driven breakdown this results in the formation of scales on the skin’s surface.

Skin Disorders

Some disorders of the skin barrier have a genetic component, such as eczema, psoriasis and ichthyosis (keratinization disorder), making damage to the skin barrier common. For example, sufferers of eczema have been shown to have a disorder in the gene that codes for filaggrin, a crucial protein for the production of NMFs. Other conditions demonstrate abnormal enzyme activity; in cases of psoriasis, atopic dermatitis and most inflammatory dermatoses serine protease activity is increased. Serine proteases regulate ceramide formation so the increased activity of these enzymes leads to a decrease in ceramides in the stratum corneum, which makes TEWL more likely.

Stress and some illnesses can also disrupt the skin’s proteolytic balance (the balance of enzymes and the molecules which inhibit their activity) also leading to faulty desquamation and a damaged skin barrier.


Dr Sebagh' Age can have a significant impact on skin barrier function by virtue of the biological changes that naturally occur as the skin ages.'   

Skin loses elasticity as it ages due to deterioration in collagen resulting from declining estrogen levels. Estrogen is crucial to the body’s process of collagen synthesis because it is a key component in the activation of fibroblasts. When activated, fibroblasts produce the key structural proteins of the extracellular matrix including collagen, elastin and fibronectin. When the skin is more fragile and less elastic it is more prone to damage. The body also produces less keratin as we age, which causes a reduction in skin’s moisture levels and this is compounded by a reduction in Hyaluronic Acid and other glycosaminoglycans also produced by fibroblast activity.

A diagram showing causes of a damaged skin barrier

Extrinsic Factors


While it is important to properly cleanse twice a day, over-cleansing, using a harsh, astringent cleanser unsuitable for your skin type, or washing your face with soaps containing Sodium Lauryl Sulfates (SLS) can affect the proteolytic balance of the stratum corneum. Subjects with soap-induced dry skin show decreased serine protease activity. Although this is the opposite trend shown in congenital skin disorders, both give rise to disrupted desquamation and an impaired skin barrier. This highlights that the delicate balance of enzymes and their inhibitors is crucial to the function of the skin barrier.

Overapplication AHA, BHA and Retinoid Products

The cause of skin barrier damage which is arguably the most common is overdoing your skincare. AHAs, BHAs and retinoid products are potential chemical irritants of which overapplication can degrade the skin barrier. Using too many actives can affect the pH level of the acid mantle which, in turn, disrupts the moisture retention capacity of the skin barrier, leading to dehydration.

Environmental Factors

Exposure of the skin to dry air, harsh weather conditions (sun and wind), extremes of temperature (moving from heated indoor spaces to low temperatures outdoors) and pollutants, are some of the unavoidable offenders in skin barrier damage and why dry skin, sensitivity and redness abound during the winter months.

How to repair and prevent skin barrier damage?

Whether the root cause is intrinsic or extrinsic, there are ways you can aid your skin’s regenerative mechanisms for repairing the skin barrier.


Making small changes to certain parts of your daily routine can have a huge impact on your skin.

It is also important to stay hydrated. While there is limited evidence to demonstrate that drinking water will directly rehydrate the epidermis, drinking water is crucial to the functioning of every cell in your body. What’s more, it has been shown that drinking water can hydrate the deeper layers of your skin which is crucial for the healthy function of the organ as a whole, and it can also help to improve skin elasticity.

There is also some evidence to suggest that a diet rich in Omega-3 fatty acids can improve the lipid composition in your skin helping to minimise its inflammatory responses. It has also been shown that ingested plant sterols (a source of healthy cholesterol) are eventually excreted to lipids in the stratum corneum after being transferred from the plasma to the skin. A diet rich in Omega-3 fatty acids, plant sterols as well as a variety of vitamins and nutrients can support the healthy function of the skin barrier all year round.

How to repair and prevent skin barrier damage


In addition to washing your skin (including your face) in lukewarm water, there are other changes you can make to your skin care routine to repair and replenish the skin’s essential barrier.


'Simplify your skincare routine, use SPF, antioxidants and environmental protective films (EPFs) and avoid harsh products and tools.'   

Firstly, it is important to simplify your skincare routine. As aforementioned, the over-application of certain active ingredients can damage the skin barrier. However, even if there was another cause, it is important to avoid AHAs, BHAs and retinol products if your skin barrier is compromised. These ingredients will irritate the skin, further depleting the lipid matrix and increasing the skin’s inflammatory response.

As part of simplifying your routine, it is also important to switch up your cleanser. Avoid any astringent ingredients whatsoever and opt for a fragrance-free milk, oil or cream cleanser. You can also limit cleansing to the evening only, particularly in cases of atopic dermatitis, eczema, psoriasis etc.


Make sure to include humectants in your skincare routine. Ingredients like Hyaluronic Acid and glycerin are hygroscopic meaning they attract and retain water helping to replenish moisture lost through an impaired skin barrier. They are also capable of influencing the phase of the lipid matrix in dry environmental conditions.

Glycerin (or glycerol) is a fantastic ingredient for a damaged skin barrier and has been conclusively proven to be a major determinant of water retention in the stratum corneum. Beyond its humectant properties, glycerin is also capable of regulating desquamation so as to keep the stratum corneum at a steady thickness throughout the shedding process. It does so by enhancing proteolytic activity near the surface to promote the dissolution of corneodesmosomes. Glycerine can also harden fragile cornified envelopes which is characteristic of an impaired skin barrier.


However, humectants on their own aren’t sufficient as any moisture added back to the skin will quickly evaporate if the lipid matrix is not replenished. Therefore it is crucial to follow any humectants with an emollient especially one rich in ceramides, cholesterol and fatty acids. This will replenish the lipid matrix whilst preventing any moisture from evaporating through the epidermis.


Finally, it is more important than ever to ensure that skin is protected when the skin barrier’s function is impaired. Your skin’s ability to protect the body from free-radical-inducing external aggressors, including UV rays, is significantly depleted and so it is important to shore up your skin’s natural defences. Increase the level of topical antioxidants particularly vitamin E which has strong anti-inflammatory and skin-soothing properties.

Niacinamide (or vitamin B3) is another ingredient which acts in an antioxidant capacity however it brings a whole host of skin barrier-repairing benefits. It has anti-inflammatory effects to soothe and calm sensitivity and redness whilst also working to repair the skin barrier by stimulating ceramide synthesis, boosting keratin production and increasing the synthesis of lipids in the epidermis.

While antioxidants can neutralise the free radicals induced by external aggressors, it is key to prevent as many aggressors and irritants from penetrating the skin as possible. When your skin barrier is damaged it is even more important to use SPF, even with the lack of sunlight in the winter. You can also help to protect your skin by using products with a biosaccharide pollution film which acts as a ‘second skin’ shielding the skin from pollutant microparticles that may penetrate the skin with an impaired barrier.

Dr Sebagh recommends...



Dr Sebagh rose de vie cream cleanser


Opt for Rose de Vie Cream Cleanser enriched with Vitamin E and nonpolar lipids to replenish the lipid matrix. It also leaves your skin protected from pollutants thanks to a polysaccharide matrix.



Dr Sebagh serum repair hyaluronic acid
Hero hydrator Serum Repair contains humectants Hyaluronic Acid and Glycerin, perfect for replenishing the water content of the stratum corneum after it has been depleted through TEWL.



Dr Sebagh rose de vie serum


Nourishing Rose de Vie Serum is ideal for sensitive and sensitised skin. With biotech ingredient Symcalmin, this serum provides the skin with a number of fatty acids thanks to numerous natural oils as well as Vitamin E. The oil creates a seal preventing any moisture attracted by humectant Serum Repair from evaporating.


When your skin barrier is damaged it is crucial to end your skincare routine with an emollient cream to seal in the benefits of your serums and minimise moisture lost through TEWL

For normal to combination skin (and male skin)...


Dr Sebagh high maintenance moisturiser


For normal to dry skin (or as your first anti-ageing moisturiser)...
Dr Sebagh vital cream moisturiser

For Eyes

The skin around the eyes is some of the thinnest on your entire body. As such, your ocular skin barrier requires some extra special care.


Dr Sebagh firming eye cream


Packed full of ceramides, humectants and fatty acids, Firming Eye Cream is the perfect product to protect delicate under-eye skin.

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