What is skin hydration?
When we speak about hydration of the skin, we don't mean the skin in its entirety, but the uppermost layer of the epidermis: the stratum corneum or the cornified layer.
The cornified layer is made up of corneocytes, which are flattened epidermal cells that are connected by specific lipids.
This skin layer has remarkable protective and defensive properties against external aggression. Only 10 to 15% of it is water. When its water concentration is lower than 10%, the skin is dehydrated.
Immediately below the cornified layer, there is a hydrolipidic film that covers the surface of the epidermis. This is an emulsion made of water and lipids that is produced by the sebaceous glands. This hydrolipidic film forms a protective coating for the skin. Its hydrophobic composition (lipids) helps the skin maintain its suppleness, improve its protection and regulate the body's water content by preventing transepidermal water loss.
Why does the skin become dry?
"Dry skin" (also called xerosis) is skin with a surface lacking in suppleness and softness. It is no longer smooth but rough to the touvh, even course and it has reduced suppleness. It peels lightly (this is called desquamation) and we therefore see small thin flakes on the surface that resemble little scales.
This dryness causes skin discomfort, tightness, tingling and even itching.
There are several causes:
- External aggression, which fall includes two categories:
- Chemical factors (soaps, antiseptics, detergents, hard water)
- Cleansing products that can alter the hydrolipidic film on the surface. This delipidating effect dehydrates the skin. Some strong, stripping soaps can even remove the hydrolipidic film. Skin dryness can therefore be linked to unsuitable hygiene products.
- Climatic factors (wind, cold, heat, UV radiation).
- In the winter season, cold dry winds trigger:
- An alteration of the hydrolipidic surface film
- An increase in transepidermal water loss
- An alteration to the desquamation process: the cold inhibits the activity of certain enzymes responsible for desquamation. The skin becomes dry and scaly. The cornified layer is altered, it can no longer fulfill its barrier function and maintain hydration in the epidermis.
- An alteration of blood circulation in the skin.
In the summer, dry heat causes dehydration of the upper layers of the epidermis, by increasing the evaporation of water from the skin.
- Aging skin.
Dry skin is a common sign of aging skin. Its incidence in the population aged over 65 is estimated at around 75%. The skin of older people typically has a thinner epidermis and slower cell renewal. Menopause, which is characterized by a hormone dysfunction, is also responsible for accelerating chronobiological aging.
- Certain skin diseases
How can we recognize the skin's degree of dryness?
The skin is a little dry
It feels rough on your finger. It has lost its satiny smooth appearance. It lacks radiance and looks dull.
The skin is very dry
It fees rough, tight and has lost its suppleness. Upon closer inspection it seems to be flaking slightly.
The skin is "ultra-dry"
It is rough, thick, scaly and cracked. This is a major problem that most likely requires special treatment.
All conditions require the help of a health professional for diagnosis and treatment