skin hydration

Why is it important to moisturize your skin?

Moisturizing our skin is part of our daily face and body routine. It is the basis of all cosmetic care. The objectives of hydration are notably when the skin becomes dry, hydration must be reinforced to restore the skin barrier by reducing the Insensible Water Loss* (PIE).


What is the skin barrier?

The skin represents a physical barrier between the body and the outside environment. It is the stratum corneum (stratum corneum), the most superficial layer of the epidermis, which ensures this protective role. It is made up of keratin, a very resistant substance (the same as that which makes up our nails and hair). The keratin is arranged like the tiles of a roof. Between these keratin lamellae are fatty substances (fatty acids, ceramides) that seal the skin, preventing water from evaporating. Water is also retained in the epidermis by substances that constitute the natural hydration factor.

The stratum corneum limits water loss and protects against chemical agents, microbes, allergens, external thermal aggression, radiation (UV), pollution, etc. For this barrier to be effective, it is important that it remains well hydrated.

A hydrolipidic film covers the surface of the stratum corneum. The water comes from sweat secretion, while the lipids come from the epidermis and sebaceous secretion. It plays a secondary role as a barrier. It is not very present in areas where there are few sebaceous glands.

Lipids fill the intercellular spaces of the stratum corneum. They accumulate on the surface of the corneocytes, and form the lipid cement. Their absence destroys the skin's barrier function. The objective of a moisturizing product will therefore be :

  • To ensure a good maintenance of the skin barrier, by reinforcing the lipidic cement.
  • To retain water, by providing humectant substances close to the natural hydration factor.


Water circulation in the skin

The skin as a whole contains 70% of water. The dermis contains more than 80% (i.e. 10% of the total water in the human body). The epidermis contains 65% of water, and the horny layer 10 to 13%.

The diffusion of water is continuous, from the dermis to the epidermis. The dermis functions like a sponge that supplies the epidermis with water. The diffusion of water then takes place through the epidermis, in a continuous and regular way, until the surface of the skin, where the water evaporates.

The dermis remains naturally hydrated. Except in exceptional circumstances, it never loses its water. It is therefore in the epidermis, and particularly in the horny layer (the most superficial layer of the epidermis), which normally contains little water, that the skin dries out. This is the target of moisturizers.


What dries out the skin?

  • Naturally, the drying out of the corneal layer intensifies with age. The skin aging is accompanied by both a reduction in the thickness of the epidermis and a qualitative alteration in the differentiation of the keratinocytes: the skin becomes rough and thinner.

  • L'daily hygiene is also frequently involved. Dryness is often caused by the use of soap or detergent gel containing irritating surfactants. Too frequent showers, especially for sportsmen and women, encourage the drying out of the corneal layer.

  • In humans, the shavingThe use of a moisturizer, followed by the application of alcoholic lotion, also dries out the skin of the face.

  • The skin is also very sensitive to climatic conditions. Cold and wind are drying factors, often accompanied by feelings of discomfort and tightness. Drying out of the skin can lead to irritant dermatitis, with the appearance of cracks on the extremities.

  • The sun plays a special role. UV rays promote an increase in the thickness of the corneal layer, which, along with the synthesis of melanin, is one of the natural ways of sun protection. However, heat intensifies evaporation and poor cohesion of the corneocytes. This results in dry skin in the summer, and often in peeling when the sun returns.

  • Some treatments can also be responsible for a global drying of the skin: It is the case for example of treatments by oral retinoids (isotretinoin, acitretin, alitretinoin) or topical treatments used for their effects against acne.

There are therefore many factors that can cause the skin to dry out. Dry skin results in an uncomfortable sensation, often causing tingling, tightness and even itching. The skin has lost its smooth surface; it is rough to the touch. It is less protected against external aggressions. This can lead to the appearance of eczema.


How to moisturize the skin?

To keep your skin well moisturized on your face, it is recommended to :

  • Cleanse your skin gently:
    • Avoid water that is too hot
    • Do not use soaps, which are too detergent. Prefer a mild dermatological cleanser, without savon, syndet type. On the face, a micellar water or milk will be preferred.

    • Always rinse well after cleaning the skin
    • Avoid the application of any substances that aggravate drying. In particular, do not apply perfume, eau de toilette or foaming antiseptic cleansers.

  • Moisturize your skin regularly with a suitable cream. There is no other way to moisturize the stratum corneum than the daily application of a suitable moisturizer.

Most moisturizing creams will act to maintain the skin barrier in good condition. They therefore contain greasy substance which will reinforce the cement between the keratin lamellae and moisturizing ingredientswhich retain water in the epidermis.

To choose your moisturizer, it is important to consider your skin type and seasons. There are creams suitable for all circumstances: rich creams for winter, for the night or when the skin is dry, and light creams for the morning, for mixed to oily skin, or for summer. In the fight against skin ageing, moisturising is the first step in giving the skin a younger appearance.

In winter the skin becomes drier and hydration must be reinforced. Cold weather disrupts the action of enzymes involved in skin metabolism and is often combined with wind, which causes the release of water from the stratum corneum and worsens water loss. This phenomenon can be accentuated by overheating, which causes dry air. Alternating too much heat inside and cold air outside further aggravates the phenomenon of skin dryness. Moisturizing the face must therefore be accentuated during the winter by using richer creams.

In summer the sunSwimming, swimming pool, sea bathing, more frequent showers, are also a source of water loss. You must not relax the hydration of the skin during the summer. This can be done with a lighter cream.

A specific texture is needed for the semi-mucous membranes of the lips. The "cream" forms are often insufficient to ensure comfort at this level. The use of a lip balm with a very lipidic texture, is necessary to protect, soothe and repair painful cracks.



*PIE: Measure of the amount of water evaporating from the surface of the skin.


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