Skin moisturization

A barrier that retains water without being waterproof

The stratum corneum is the most superficial part of the epidermis. It combines flattened cells, corneocytes, and lipids organized together. It is often compared to a wall: the cells are the bricks and the lipids are part of the mortar. This image helps to understand the protection it provides, even if the real structure is more complex and remains in constant renewal.

Water continually crosses this barrier and evaporates: this is the imperceptible loss of water, or transepidermal water loss, distinct from perspiration. When the barrier is altered, or external conditions favor dryness, the stratum corneum may lack water. It becomes less flexible, rougher and sometimes uncomfortable. The moisturizer mainly acts on this surface balance, without having to penetrate deeply to be useful.

Humectants: retain water

Glycerin, urea and hyaluronic acid are among the humectants used in treatments. Their affinity with water helps retain it in the surface layers. This is why these ingredients are often combined with components that limit water loss.

The skin also has its own hydrophilic substances, grouped under the name of natural hydration factors, or NMF. They include in particular amino acids and derivatives resulting from the degradation of proteins such as filaggrin. They help maintain the flexibility of corneocytes. Irritant exposures can change this pattern, which helps explain why skin that is cleansed too aggressively sometimes becomes rough despite the water used to wash it.

Emollients, occlusives and lipids: complementary roles

Emollients improve the feel and flexibility of the surface. Occlusive agents further slow down the departure of water by forming a protective film; Vaseline is a classic example. These categories are not watertight boxes: the same ingredient can fulfill several functions. A balanced cream can therefore provide a soft sensation while helping the stratum corneum retain its water.

Ceramides, cholesterol and fatty acids naturally participate in the organization of lipids between cells. Certain formulas are inspired by it to support the skin barrier. Their presence is interesting, but the effectiveness depends on the entire treatment. A long list of expensive ingredients is no substitute for a well-tolerated formula, and a simple cream can significantly improve ordinary dryness.

Why oily skin can also feel tight

Sebum comes from the sebaceous glands and contributes to the film present on the surface. Its quantity is not a direct measure of the water contained in the stratum corneum. You can therefore have a shiny nose and tight cheeks, particularly under the effect of a cleanser or a drying treatment. Adding light care then meets a need for comfort; This does not mean covering the entire face with a very rich texture.

The terms “dry skin” and “dehydrated skin” are useful in cosmetic language, but do not always refer to two clearly separate situations. Dryness can combine lack of water, disorganization of lipids and irritation. Rather than making a diagnosis based on a few tensions, observe what accompanies them and what improves them. Persistent symptoms may require evaluation, especially if there are patches or itching.

The effect on appearance and its limits

When the stratum corneum regains flexibility, the small scales and fine lines linked to dryness can become less visible. The skin then appears smoother, sometimes more luminous. It is maintained above all as long as the conditions which promote good hydration are met.

An oil alone can soften the skin and, depending on its composition, limit part of its water loss. However, it does not reproduce all the action of an emulsion containing water, humectants and protective agents. Likewise, spraying water provides a cool feeling without providing long-lasting hydration alone. The choice therefore depends on the need: an immediate pleasant sensation and an improvement that lasts throughout the day are not always the same thing.