All you need to know about cutaneous xerosis.

The term cutaneous xerosis is a scientific term used to describe extreme skin dryness, caused by a disruption in the skin barrier. It is characterised by skin that feels rough to the touch, appears dull and is flaky, with occasional micro-cracks or deep fissures in more severe cases. Feelings of tightness, discomfort and itching are common, particularly after contact with water or in cold environments or dry conditions. In some instances, the skin becomes thinner and is highly vulnerable, which can lead to the onset of redness or irritation patches. In older individuals, xerosis can worsen and progress to deep cracks, particularly on the legs and hands.

Although it can be temporary and related to weather conditions, xerosis is sometimes a sign of a skin imbalance associated with a pathology. Indeed, it is often associated with dermatoses, such as the eczema or the psoriasis, but also with metabolic disorders, such as diabetes or chronic kidney failure, hence the importance of not neglecting this warning signal launched by the skin.

As stated above, xerosis is primarily caused by an impairment of the skin barrier, which manifests at various levels of the stratum corneum, the outermost layer of the skin. This layer is mainly composed of corneocytes surrounded by a lipid matrix and plays a key role in skin protection, alongside the hydrolipidic film. However, in the case of xerosis, their effectiveness is limited, due to a low presence of lipids and natural moisturising factor (NMF), as well as a reduced sebum synthesis.

• Xerosis: a reduction in the lipids of the stratum corneum.

  Intercellular lipids, primarily ceramides (50%), cholesterol (25%) and free fatty acids (10-20%), form a matrix that binds corneocytes together, thus creating a barrier that limits water loss and the entry of pathogens. However, when lipid production is reduced, as is the case in xerosis, insensible water loss increases, which makes the skin rougher and more fragile.

• The natural moisturising factor is reduced in cases of xerosis.

  The term NMF refers to the collection of hygroscopic substances responsible for maintaining hydration in the stratum corneum of the epidermis. It is primarily composed of amino acids, most of which are derived from the hydrolysis of filaggrin in the stratum corneum. Individuals suffering from xerosis have a reduced NMF, which decreases their skin's ability to retain water, making it drier and less flexible. The various compounds of the NMF indeed contribute to the plasticity of corneocytes, preventing cracks and excessive flaking, characteristics of dry skin.

On average, the water content of the stratum corneum is about 15 to 20%. However, it is less than 10% in skin affected by xerosis.

• The hydrolipidic film is compromised in cases of xerosis.

  Finally, in individuals suffering from xerosis, sebum synthesis is reduced, leading to an alteration of the hydrolipidic film. This film, located on the surface of the epidermis, is the primary protective barrier between the skin and its external environment. It is predominantly composed of water, derived from sweat, and fat, derived from sebum. When the production of the latter is insufficient, as is the case in individuals affected by xerosis, the hydrolipidic film becomes more fragile and can no longer effectively fulfil its protective function. The skin then becomes more prone to dehydration and irritation.

The deterioration of the skin barrier observed in cases of xerosis results from internal and external factors that disrupt the skin's hydrolipidic balance. The first factor is age. Indeed, over time, the production of ceramides, cholesterol and fatty acids, essential components of the intercellular cement, decreases. This scarcity weakens the cohesion of the corneocytes, making the skin more permeable to water evaporation. Simultaneously, sebum secretion slows down, which weakens the hydrolipidic film.

Environmental conditions also play a significant role. A cold and dry air, whether in winter or due to inappropriate air conditioning, accelerates water loss by disrupting the lipid structure of the stratum corneum. Furthermore, wind and exposure to UV rays damage the epidermal lipids, particularly polyunsaturated fatty acids, leading to a degradation of the barrier function and a reduced ability of the skin to retain moisture.

Finally, certain daily habits can exacerbate xerosis. The overly hot showers dissolve the protective lipids of the hydrolipidic film, making the skin more vulnerable to external aggressions. The use of certain soaps, particularly those containing sulfates such as sodium lauryl sulfate (SLS), further damages the skin barrier by eliminating epidermal lipids and altering the skin's pH, which weakens the enzymes involved in the maturation of cells in the horny layer.

The cutaneous xerosis can be effectively managed through the regular and long-term use of moisturising and nourishing creams. The solutions to xerosis rely on three main types of active ingredients: humectants, film-forming agents, and emollients, each working at their level to restore the integrity of the skin barrier.

• The humectants : Humectants are substances that attract water into the skin. Glycerine is one of the most commonly used and effective humectants in cases of xerosis, due to its high hygroscopicity, lipid-modulating activity and corneodesmolytic effect, meaning it facilitates the maturation of the corneocyte envelope by transglutaminase. Glycerine also promotes skin hydration by attracting and retaining water in the superficial layers of the epidermis. Other humectants, such as urea or components of the NMF, are also frequently used to combat xerosis.

• The film-forming agents : Film-forming agents work by creating a protective layer on the surface of the epidermis, thereby preventing the evaporation of water from the skin and strengthening the hydrolipidic film. It should be noted that film-forming agents can be hydrophilic, showing an affinity with water, or hydrophobic, repelling it. Hydrophilic agents, such as carbohydrates, capture water molecules to create a hydrogel and form a hydrated film on the skin's surface. Hydrophobic film-forming agents, such as silicones, mineral or vegetable oils, and waxes, have a more occlusive effect and block trans-epidermal water loss more by opposing water molecules.

• The emollients : Emollients are ingredients that soften and smooth the skin, while enhancing its elasticity and suppleness. More specifically, emollients promote the accumulation of water in the stratum corneum and strengthen the cohesion between the lipids in the intercellular space, particularly ceramides, in order to hinder the movement of water within the stratum corneum. Some of them, such as vegetable oils, can insert themselves between the lipids of the stratum corneum and reinforce the barrier function of the epidermis.

The daily application of creams containing humectants, film-forming agents, and emollients can compensate for a lack of lipids and improve the skin's hydration and barrier function. Scientists agree that a combination of hydrophilic and lipophilic molecules is preferable.

Product recommendations?

To care for dry to very dry skin, we offer at Typology a dermatological soap and a lipid-replenishing balm. Enriched with calendula extract and sweet almond oil, our dermatological soap gently cleanses the skin without compromising its hydrolipidic film. It is formulated at a neutral pH and does not contain soap or sulfates. As for our lipid-replenishing balm, it is a high-tolerance treatment providing continuous hydration for 24 hours, while reducing feelings of discomfort and extending the periods between severe dryness.

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• ROBETS M. S. & al. Skin biology, xerosis, barrier repair and measurement. Drug Discovery Today: Disease Mechanisms (2008).

• GIMÉNEZ-ARNAU A. & al. Xerosis: a Dysfunction of the Epidermal Barrier. Actas Dermo-Sifiliográficas (2008).

• STAUBACH P. & al. Diagnosis and treatment of xerosis cutis – a position paper. JDDG: Journal der Deutschen Dermatologischen Gesellschaft (2019).

• KOTTNER J. & al. Molecular characterization of xerosis cutis: A systematic review. Plos One (2021).