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EXPERT’S NOTEBOOK

Dryness and dehydration

What is dehydrated skin?

Whether your skin is naturally dry, combination, normal or oily, external aggressors can cause it to become dehydrated.

It is the body’s first line of attack from the external environment, such as physical aggressors (shocks, temperature variations, wind, etc.) or chemical aggressors (surfactants, irritants, etc.).

Dehydrated skin looks dull, feels rough, flaky and is sometimes lined or cracked.

Skin “types” 

While the entire human body, including the dermis, is made up of 60% water, this is not the case for the epidermis, whose surface layer acts like an interface between the very humid internal environment and the much drier external air. The epidermis contains 20 to 30% water, and its most superficial layer, the stratum corneum, 10 to 20%. This stratum corneum has a specific structure, often compared to a brick wall (corneocytes) and cement (intercellular lipids), whose role is to prevent water from evaporating from the body.

Some skin types are naturally better hydrated, or less dry, than others. Dry skin, whether it is simple xerosis, xerosis as a result of atopic dermatitis, or ichthyosis, contains much less water than normal skin. This dryness is due to abnormalities in lipid metabolism (ceramides), protein metabolism (proteases, filaggrin) or even impaired epidermal differentiation.

A drop of spring water

 

The various common and pathological dry skin types

Simple xerosis

The most common, easily corrected by applying emollients.

Senile xerosis

More marked on the limbs than simple xerosis.

Induced xerosis

Skin dehydrated by products containing overly aggressive surfactants (soaps). Similarly, irritating treatments (retinoid, fruit acids) dry out the skin.

Winter xerosis

An escalation of simple xerosis, under the influence of the cold and wind.

Atopic xerosis

Atopic dermatitis, or eczema in children, includes more or less pronounced skin dryness. Linked to structural abnormalities in the epidermis, this dryness is responsible for allergens penetrating and loss of water through the epidermis. Some serious nutritional deficiencies can cause or worsen skin dryness. Some general conditions can cause skin dryness.

Ichthyosis

Rare genetic conditions, genetic or acquired, of varying severity.

Our expert answers your questions

Living better with dry and dehydrated skin

The two main causes of dry skin are external or internal.
External causes:
- Climatic: wind, cold, excessive sunshine, lack of humidity in the atmosphere (air-conditioning, heating).
- Chemical: products with too much detergent, topical medical treatments, unsuitable cosmetics.
- Mechanical: shaving and waxing.
- Internal causes:
- Physiological: skin ageing
- Pathological: skin conditions affecting the skin barrier.

Yes, but not just water: we cannot rehydrate the superficial layer of the epidermis simply by drinking water or by wetting the skin. Lipids (fats) are also essential for retaining water.

Yes, this is one of the causes of dry skin. Sun exposure is an attack (burn) in which the epidermis reacts by producing more pigment (a tan) and thickening. The dryness observed is temporary due to increased water loss.

Yes. Some domestic water supplies have a high limescale content: this is known as “ hard ” water. They can increase the drying effect of skincare products. You can soften water by using special devices or compensate for hard water by using ultra-rich products.

Dehydrated skin is dull and tired. It feels rough with dehydration lines. Skin is fragile and lacks suppleness.

There are two reasons for this:
a lack of water with less than 10% water in the outermost layer of the skin (stratum corneum) and an impaired barrier function.

The aim is to nourish and hydrate the skin by limiting damage and irritation. When showering, avoid soap and opt for ultra-rich cleansers or gels enriched with protective and hydrating ingredients. Use emollient creams to hydrate and nourish the skin, and ensure the epidermis is intact, which is essential for its protective barrier function. Applying these emollients regularly is important. Ideally, every day.

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