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Pourquoi a-t-on la peau sèche ?

Why do we have dry skin?

Dry skin is a skin type that is characterized by its roughness and tightness. This skin dryness can be innate, favored by certain weather conditions or by aging. Discover in this article all the causes of dry skin.

Summary
Published February 16, 2024, by Pauline, Head of Scientific Communication — 6 min read

Dry Skin: How to Identify It?

A dry skin lacks hydration and nutrition. More precisely, skin dryness is characterized by an alteration in cellular cohesion, a deficiency in natural moisturizing factors (NMF), and a deficiency in the production of fatty substances. In dry skin, the production of sebum by the sebaceous glands is insufficient. This leads to an imbalance of the hydrolipidic film. This film is normally located on the surface of the epidermis and contributes to maintaining its hydration, as well as protecting it against external aggressions such as wind, cold, or pollution. Finally, the synthesis of ceramides, lipids that play a role as intercellular cement, is reduced in dry skin, which impacts the barrier function of the epidermis.

A dry skin is particularly prone to irritations. This type of skin is also recognized by its roughness, its dull appearance, its lack of suppleness, its tendency to flake, as well as the presence of tightness. In extreme cases, redness, cracks, and fissures can appear.

Let's note that the terms "dry skin" and "dehydrated skin" refer to two different conditions. Dry skin is a skin type that lacks lipids, while a dehydrated skin is a skin condition that lacks water.

What are the causes of dry skin?

An insufficient sebum production is the main cause of skin dryness. It results from both internal and external factors.

  • Hereditary.

    In some individuals, skin dryness is due to a genetic predisposition. Indeed, a mutation on the gene coding for the filaggrin protein is often responsible. This protein is normally expressed in epidermal cells and helps to maintain the skin barrier function.

  • Hormonal fluctuations.

    The production of sebum is also influenced by hormonal factors. Thus, it is possible for the skin to become dry during puberty, pregnancy, or menopause, periods when significant hormonal variations occur. Indeed, female sex hormones, the estrogen and progesterone, are closely linked to aging and skin dryness. Estrogens, in particular, stimulate the synthesis of collagen and elastin by fibroblasts, structural proteins of the epidermis. As for progesterone, it stimulates the production of sebum by the sebaceous glands, which promotes the maintenance of the skin's hydrolipidic film. At menopause , for example, the synthesis of estrogen and progesterone by the ovaries is halted. This causes a decrease in sebum production, and thus a weakening of the hydrolipidic film. The skin is then more exposed to dryness.

  • Certain skin conditions.

    The psoriasis or eczema can also be responsible for skin dryness. These chronic inflammatory diseases often manifest themselves through the appearance of red patches and skin dryness. The causes of these conditions remain largely unknown, but it appears that the risk factors are primarily of two types: genetic and infectious.

  • The natural agingprocess.

    The skin's ability to produce sebum decreases with age. Indeed, the activity of the sebaceous glands weakens in our thirties, which compromises the hydrolipidic film. The synthesis of ceramides also begins to decrease, impacting the skin barrier. Additionally, the level of hyaluronic acid also gradually decreases, starting in our twenties. This molecule plays a key role in skin hydration and is notably capable of retaining up to 1,000 times its weight in water.

  • Some environmental factors.

    External factors can also contribute to skin dryness. Prolonged exposure to the sun or to dry and icy air in winter can weaken the epidermis. These elements can cause the degradation of the hydrolipidic film that protects the skin. This film tends to thin out and can no longer perform its function properly.

  • The use of unsuitable products.

    When one has dry skin, it is recommended to favor gentle, nourishing, and lipid-replenishing treatments, and to avoid any product containing matifying active ingredients such as zinc or azelaic acid. The use of alcohol derivatives and synthetic fragrances is also discouraged, as these products are drying.

  • Hard water.

    After a shower with hard water, feelings of skin tightness may occur, accompanied by various issues such as irritations, itching, or even the appearance of red patches. The explanation is as follows: the calcium and magnesium ions, which make up hard water, form microcrystals on the skin, causing the prickling sensations.

Sources

  • BONTE F. & a. Skin hydration: a review on its molecular mechanisms. Journal of Cosmetic Dermatology (2007).

  • SCHMELZ M. & al. Skin barrier damage and itch: review of mechanisms, topical management and future directions. Acta Dermatologies-Venereologica (2019).

  • TAKAMORI K. & al. Mechanisms and management of itch in dry skin. Acta Dermatologies-Venereologica (2020).

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