Why does skin become dry with age?

Skin aging is an inevitable process primarily due to a degradation of skin components, whether in the epidermis, dermis, or hypodermis. Indeed, as we age, the skin undergoes several changes in its structure and function, contributing to its dryness.

• With age, the skin loses its ability to retain water in its superficial layers.

  The skin thins and becomes more fragile over time. This thinning promotes the evaporation of water located in the outer layers, giving the skin a drier and rougher appearance. Indeed, in young skin, the horny layer can store between 10 and 20% of the body's water. In mature skin, this percentage can drop below 10%, depending on internal and external hydration levels. The skin thus gradually loses its ability to retain water with age and becomes dehydrated. All of these changes lead to the appearance of aging signs such as wrinkles and fine lines.

• Over time, the production of hyaluronic acid decreases.

  The hyaluronic acid, primarily produced by the dermal fibroblasts but also at the epidermal level, is a significant source of hydration. It acts like a sponge and is capable of retaining substantial amounts of water. However, over time, the hyaluronic acid content in the skin is reduced, as well as its quality. The hyaluronic acid level decreases by about 6% every 10 years. Thus, by the age of 50, the level of hyaluronic acid naturally present in the body has dropped by half, contributing to skin dryness.

• The amount of intercellular lipids decreases with age.

  Intercellular lipids play a fundamental role in maintaining skin hydration and protecting the skin against external aggressions. These lipids, primarily composed of ceramides, cholesterol, and free fatty acids, form the lamellar bilayers of the stratum corneum, the outermost part of the epidermis. Their organization into ordered structures allows for the trapping of water within the epidermis and limits insensible water loss.

  However, over time, the synthesis and quantity of these lipids significantly decrease, leading to a gradual deterioration of the skin's barrier function. This reduction compromises the skin's ability to retain moisture, making it drier and more vulnerable to irritants, allergens, and pathogens. Moreover, a weakened skin barrier impacts the skin's ability to regenerate effectively, which slows healing and promotes the occurrence of chronic irritations. This weakening partly explains why older individuals are more susceptible to environmental assaults, such as cold, pollution, or humidity fluctuations, which exacerbate skin dryness.

• The levels of natural moisturizing factors (NMF) decrease with age.

  Natural Moisturizing Factors, or NMFs, are essential components for maintaining skin hydration. Present within the corneocytes of the stratum corneum, they are primarily composed of amino acids, as well as their derivatives and other hygroscopic molecules capable of attracting and retaining water. NMFs play a key role in the preservation of skin hydration. However, as time passes, the production of NMFs gradually decreases, reducing the skin's ability to retain water and thus contributing to skin dryness, as well as the onset of tightness and loss of elasticity.

• The function of the sebaceous and sweat glands weakens over time.

  Over time, the activity of the sebaceous glands decreases. These glands, by producing sebum, play a key role in maintaining skin hydration. It's important to remember that sebum is part of the hydrolipidic film of the skin, forming a protective barrier on its surface and limiting the evaporation of water from the stratum corneum. The natural decrease in sebum production therefore makes the skin drier and more vulnerable to external aggressions.

  Simultaneously, the sweat glands, which are responsible for sweat production, also experience a slowdown in their activity. Sweat contains elements essential to the skin's water balance, including electrolytes and natural moisturizing factors. A decrease in perspiration with age thus contributes to a deterioration of skin hydration and a reduction in the skin's natural defenses. When the secretion of sebum and sweat becomes insufficient, the hydrolipidic film no longer effectively fulfills its barrier role, and the skin gradually loses its ability to retain water, resulting in skin dryness.

• Hormonal variations in women contribute to skin dryness.

  Adding to these various elements is the decline in estrogen and progesterone levels in women during menopause, leading to profound changes in skin structure. Indeed, estrogens normally act by stimulating fibroblasts, the dermal cells that contribute to the synthesis of hyaluronic acid, collagen, and elastin. The decrease in the production of these molecules results in a loss of skin suppleness and elasticity, as well as the onset of skin dryness. The effects of progesterone on the skin are less well understood, but it is suggested that this steroid hormone upregulates the synthesis of sebum by the sebaceous glands. As mentioned above, sebum is an essential component of the hydrolipidic film found on the surface of the epidermis, and its decrease makes the skin more fragile and dry.

Several factors contribute to skin dryness associated with aging. Fortunately, adopting a tailored skincare routine, rich in moisturizing and nourishing active ingredients, helps to maintain the comfort and suppleness of the skin.