Common misconceptions about the skin barrier.

False.

The skin barrier does not respire in the biological sense of the term. Unlike the lungs, it does not take up oxygen from the air to redistribute to the cells. The oxygen used by keratinocytes and fibroblasts comes from the blood circulation in the dermis, not from the outside. This confusion arises because the skin exchanges with the environment, allowing certain lipophilic molecules to pass through the stratum corneum, but this diffusion is very limited. Thus, saying that the skin "breathes" is a misleading metaphor.

This myth often fuels the fear that creams or makeup can ‘suffocate’ the skin. In reality, the only risk posed by very rich or occlusive products is the obstruction of pores, those tiny openings connecting the sebaceous glands to the surface of the epidermis. Sebum can then accumulate, form a plug and encourage the formation of blemishes, particularly in oily skin. However, this phenomenon has nothing to do with skin that ‘no longer breathes’: the skin barrier is never actually suffocated, even when the complexion appears dull.

True and false.

It is an oversimplification to equate the skin barrier with the hydrolipidic film. In reality, the skin barrier corresponds to the combination of the hydrolipidic film and the intercellular lipid layer present in the stratum corneum. The hydrolipidic film is the thin superficial layer composed of sebum and sweat, which provides immediate protection against external aggressors and contributes to hydration of the skin surface. The intercellular lipids, for their part, structure the stratum corneum and, together with the hydrolipidic film, limit water loss and the entry of pathogens. These two components play complementary roles in the skin’s barrier function.

False.

The skin barrier has functions beyond merely preventing water loss. In addition to this role, it helps protect the skin against the entry of pathogens, such as bacteria, viruses or fungi, thereby reducing the risk of infection and inflammation. The intercellular lipids of the stratum corneum and the hydrolipidic film actively contribute to this defence by forming a physical and chemical barrier, which regulates what can penetrate the skin.

Good to know : Beyond its role as a barrier against dehydration and microbes, the skin performs numerous essential functions. It contributes to the immune response, sensory perception, thermoregulation, and vitamin D synthesis...

False.

The skin microbiota plays a central role in the health and resilience of the skin barrier. This complex ecosystem, composed of bacteria, yeasts and viruses living on the skin surface, continuously interacts with keratinocytes and immune cells. These exchanges contribute to the regulation of inflammation and the maintenance of an acidic pH. Moreover, commensal bacteria, such as Staphylococcus epidermidis, produce organic acids and antimicrobial substances that prevent the proliferation of pathogenic species, such as Staphylococcus aureus.

An imbalance of the microbiome, known as dysbiosis, conversely weakens the skin barrier and promotes inflammation. This is, for example, what happens in certain forms of eczema, where microbial diversity diminishes in favour of S. aureus, which stimulates immune responses. This process sustains inflammation and exacerbates water loss.

The microbiota can be regarded as a living extension of the cutaneous barrier.

False.

Indeed, the skin barrier tends to weaken with age. Over time, the skin undergoes structural changes: the epidermis and dermis become thinner, cell renewal slows, and both the number and activity of immune cells decrease… These changes reduce cellular cohesion and repair capacity, making the skin more susceptible to irritations, infections and dehydration. Filaggrin production also drops due to slower turnover; filaggrin is a stratum corneum protein that aggregates corneocytes. In addition, low-grade chronic inflammation sets in. Extrinsic factors such as UV exposure, which accelerate skin ageing and further weaken barrier function.

However, despite these changes, it remains entirely possible to maintain a healthy skin barrier as we age. Studies have shown that the regular use of gentle cleansers, such as dermatological cleansing bars, and moisturising and relipidating treatments significantly enhance barrier integrity. Slightly acidic formulations containing ceramides, glycerol or urea help limit xerosis and pruritus commonly experienced by mature skin. Finally, topical antioxidants can complete the skincare routine by supporting the skin’s natural defences.

Ageing does not inevitably result in a loss of skin barrier function, provided that appropriate skincare is used.

False.

While the skin does begin to repair itself swiftly after damage, complete restoration of barrier function requires far more time. Generally, it takes around 3 weeks for the skin barrier to naturally regain its functional integrity, depending on the extent of the damage. The initial hours are devoted to re-establishing the continuity of the skin surface, but lipid reconstruction, pH normalisation and the restoration of cell cohesion proteins necessitate a longer, gradual process.

Scientific evidence

A study conducted on 32 healthy volunteers illustrated this slow pace of regeneration. The researchers induced small 8 mm suction wounds on the forearm and then monitored their progression. Measurements showed that re-epithelialisation was almost complete after eight days, but barrier function, assessed by water loss, did not return to normal until around three weeks. Moreover, persistent changes, such as a post-inflammatory hyperpigmentation and increased stiffness of the skin tissue, were observed up to 60 days after the injury. This suggests that newly formed skin remains more vulnerable and potentially prone to new lesions.

Tip : Regular application of hydrating and reparative treatments can accelerate the regeneration of the skin barrier.

False.

The cosmetics require time and patience to yield results. While it is true that some products can quickly enhance hydration and reduce water loss from the very first application, these effects primarily reflect a superficial and transient action. Moisturising creams operate through different mechanisms, mainly via a humectant effect (retaining water in the stratum corneum), an emollient effect (supplying lipids) and an occlusive effect (forming a protective film that limits evaporation). These effects help to relieve sensations of discomfort and to partially restore the skin barrier, but true structural repair, that is the restoration of intercellular lipids and corneocyte integrity, cannot occur instantaneously.

Studies show that full restoration of the skin barrier requires several days to several weeks of regular use of moisturising products. The most pronounced improvements in barrier function are typically seen after 2 to 4 weeks of daily application. Efficacy also depends on the product formulation and its compatibility with the skin type: poorly suited products can paradoxically further impair the skin barrier.

False.

A damaged skin barriercan be repaired, provided suitable skin care treatments are used that support its physiological regeneration mechanisms. The previously cited studies clearly demonstrate this: the regular application of moisturising creams enriched with lipids, urea or vegetable oils significantly improves hydration, reduces water loss and restores the lipid composition of the stratum corneum, leading to improved barrier function after a few weeks of use.

Scientific evidence

A clinical study investigating a biphasic serum containing 17.5% plant oils, 61% water, 2% panthenol, 2.7% glycerine and hyaluronic acid demonstrated the benefit of this type of treatment in repairing the skin barrier. The trial, conducted with eight volunteers over 14 days, measured insensible water loss and variations in stratum corneum hydration. The table below shows the results obtained, which reflect a significant and rapid improvement in skin barrier function in the group using the biphasic serum, whereas no significant change was observed in the control group.

Note : For atopic-prone skin or skin suffering from xerosis, barrier repair may be slower and more delicate owing to chronic alterations of the hydrolipidic film and a deficiency of lipids and natural moisturising factors. However, even in these cases, targeted care gradually restores the integrity and function of the skin barrier.

False.

A weakened skin barrier is not always visible to the naked eye. Sensations of discomfort, such as tightness or warmth, can, for example, be a non-visible sign. Furthermore, numerous studies have shown that alterations in barrier function can occur even on skin that appears normal, without redness, dryness or any apparent lesions. These dysfunctions are often detectable only through instrumental techniques, such as measuring transepidermal water loss (TEWL). For example, some individuals with eczema exhibit elevated TEWL or an altered lipid profile even in skin areas that appear healthy.

Scientific evidence

Researchers in a study of 22 children with atopic dermatitis and 40 healthy children observed in the atopic group a significant increase in transepidermal water loss (TEWL) and a decrease in stratum corneum lipids, two indicators of impaired barrier function. Interestingly, TEWL was also higher in apparently normal skin areas (without visible lesions), although to a lesser extent than in eczematous regions. The level of squalene, one of the main lipid components of sebum, was likewise reduced, even in these non-inflammatory areas.

Skin barrier dysfunction may precede visible signs, and apparently healthy skin can already harbour underlying fragility.

True and false.

It is true that the sensation of tightness very often stems from an alteration of the skin barrier. Indeed, when the cohesion between corneocytes decreases or when the hydrolipidic film loses efficacy, water evaporates more readily through the epidermis. In parallel, the skin becomes more permeable to irritating agents, which stimulates cutaneous nerve endings, hence the sensation of tightness or even tingling. This phenomenon is particularly common after using overly harsh cleansers, during exposure to cold, wind or low ambient humidity, or when the skin lacks lipids to maintain its barrier function, as can occur in skin prone to the xerosis.

Apart from a truly compromised skin barrier, the sensation of tightness can also originate from an allergic reaction. This occurs after the skin is exposed to an allergen that triggers local inflammation, without necessarily causing any structural disruption to the skin barrier. Furthermore, in sensitive skin, the discomfort may be due to hyperactivity of the nervous system, again without necessarily compromising the barrier.

False.

It is entirely possible to have a compromised skin barrier, even with oily skin. This may seem contradictory at first glance: oily skin secretes sebum abundantly, which contributes to the composition of the hydrolipidic film. Situated at the surface of the epidermis, this film limits water loss and helps maintain a balanced skin barrier. However, its effectiveness does not depend solely on the hydrolipidic film but also on the intercellular lipid layer of the stratum corneum. In oily skin, this layer can become disorganised, leading to an alteration of the skin barrier.

Scientific evidence

A recent study conducted on 47 individuals with oily, sensitive skin confirmed that this skin type indeed exhibits a measurable impairment of the skin barrier. The researchers analysed several skin parameters – hydration, transepidermal water loss, sebum secretion and erythema – as well as the metabolome of the stratum corneum, corresponding to the full complement of metabolites. The results revealed a significant decrease in sphingolipids and ceramides, molecules that intercalate between the cells of the stratum corneum to maintain their cohesion and the stability of the skin barrier.

For example, the concentration of sphingomyelin SM(d18:1/16:0) was reduced by nearly 68% in moderately sensitive oily skin and was virtually absent in highly sensitive oily skin. This decrease in structural lipids, the cause of which remained unidentified, was accompanied by an imbalance in the metabolism of amino acids and sphingosines, indicative of an overall weakening of the skin’s barrier function.

In other words, even oily skin can suffer from latent inflammation and exacerbated sensitivity, demonstrating that excess sebum and an effective skin barrier do not always go hand in hand.

False.

The ceramides are not the only actives capable of restoring the skin barrier, even though they are major components of it. The squalane, for example, reinforces the hydrolipidic film through biomimicry. Likewise, plant oils, rich in fatty acids, can fortify the hydrolipidic film or even embed within the stratum corneum to strengthen its cohesion in some cases. The natural moisturizing factors (NMF), a mixture of amino acids and urea, help to maintain water in the stratum corneum and can also aid in restoring the skin barrier.

Scientific evidence

Several studies have shown that ceramide-free formulations can significantly improve skin barrier function. Notably, a clinical study was conducted on 25 individuals with dry, atopic skin. The participants applied a cosmetic formulation at physiological pH containing 10% urea and sweet almond and evening primrose oils for three weeks.

The measurements demonstrated a significant improvement in skin hydration, a tendency towards pH normalisation, and a visible reduction in dryness. Lipid analysis of the stratum corneum revealed an increase in total lipid content, notably of ceramides EOS, NP and AP.

False.

No scientific evidence supports this idea; in fact, the opposite is true. Washing your skin too often, especially with soap and water, weakens the skin barrier. Numerous studies show that each wash increases transepidermal water loss, raises the skin pH, and accentuates redness and irritation. These effects are cumulative: the more you wash, the weaker your skin becomes. The skin thus does not become more resistant with repeated washing.

Scientific evidence

A study conducted with 15 volunteers illustrates this phenomenon. Each participant tested six different washing and drying techniques applied to the forearm, combining water or soap with drying by friction, tapping or evaporation. The researchers measured transepidermal water loss (TEWL), hydration, pH and erythema after each step. The results are unequivocal: simply washing with water or soap increases TEWL, and this effect intensifies with each successive wash.

For example, a soap wash followed by towel drying caused TEWL to increase from 10.1 to 13.1 g/h·m² after just two washes. Even air drying or patting, often perceived as gentler, led to a marked increase in TEWL, up to 30.1 g/h·m² in some cases. Moreover, the skin’s pH, normally acidic (around 5), rises above 6.0 after two soap washes, indicating a weakening of the skin’s antimicrobial defence.

Hygiene is, of course, essential, but to preserve the skin barrier, we recommend favouring mild cleansers with a physiological pH and applying a moisturiser after each wash to restore the skin’s hydrolipidic film. Furthermore, do not exceed one shower per day.

False.

Excessive exfoliation can significantly impair the skin barrier. By frequently removing dead cells from the stratum corneum, its integrity is compromised, making the skin more susceptible to irritants, pathogens, and dehydration. Several studies suggest that overly frequent or aggressive exfoliation contributes to the increase in barrier function impairments observed in industrialised societies. Following exfoliation, the skin barrier is weakened: hence it is advised to apply a moisturiser afterwards.

On the other hand, exfoliation should not be excluded from one's skincare routine. A gentle and controlled exfoliation allows the removal of excess keratinised cells that could disrupt the cohesion of the stratum corneum and improves the absorption of topical treatments. Indeed, this process, naturally regulated by enzymes such as kallikreins that degrade corneodesmosomes to allow desquamation, decreases with age, hence the importance of supporting it. However, ensure you use a chemical or physical exfoliant suited to your skin type (no AHAs for sensitive skin, no mechanical scrubs with large grains for damaged skin...).

One to two exfoliations per week are sufficient to support skin regeneration without compromising the skin's barrier function.

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