1- What is skin hydration, and why do we want to have hydrated skin?
The hydrolipidic barrier of the outermost layer of the epidermis prevents skin dehydration, ensuring natural hydration of the skin.
When this barrier is in poor condition, the skin dries out.
The skin is considered hydrated if the water content of the stratum corneum is high. Hydrated skin helps prevent the appearance of dullness, protects against premature ageing and skin dryness.
2 – How a cosmetic product works to hydrate the skin
The role of a hydrating product is to act on the surface of the skin. It acts at the cellular level via different biological modes of action. The active ingredient present in the cosmetic product will attach to the stratum corneum by dissolving in its surface hydrolipidic film. It then crosses this barrier in two possible ways: absorption by the stratum corneum or by the cutaneous appendages.
Another way to guarantee hydrated skin is to prevent the skin’s natural water from escaping. Cosmetic products that have a film-forming effect physically limit water loss (occlusive effect).
3 – How do you measure the level of skin hydration?
Water content is measured using a corneometer. A probe measures the electrical capacitance of the skin to conduct as a dielectric. As the high dielectric constant of the skin is partly linked to the water content of the tegument, measuring the skin’s electrical properties can evaluate the state of hydration of the superficial layers of the epidermis. Repeated measurements of electrical capacity thus allow us to objectively evaluate the effect of cosmetic products on the water balance and state of hydration of the skin (comparison control zone / treated zone): it measures skin hydration kinetics.
4 – What about film-forming products?
When the skin barrier is damaged, water from the skin’s outer layer escapes, drying out the skin. Film-forming products aim to “repair” this damaged skin barrier. As soon as the skin barrier is damaged, water loss increases. The measurement of the water that evaporates on the surface of the skin is called the TEWL measurement: Transepidermal Water Loss: the less evaporated water the sensor of the tewametry probe measures, the more the skin is hydrated.
The main role of a cosmetic care product is to provide skin comfort. The hydrating effect is one of the effects most sought by users.
In the test laboratory, measuring the hydrating effect of a cosmetic product is easy to do, fast and economical. At COSMEPAR, test sessions take place every fortnight, without reservation!
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