Lactic acid, an acid suitable for dry skin (-).

The hydroxy acids are widely used in cosmetics. Depending on their chemical structure, there are several types:

• Alpha-hydroxy acids (A.H.A.) including glycolic acid, lactic acid, mandelic acid, citric acid... ;

• Beta-hydroxy acids (B.H.A.) with salicylic acid;

• Polyhydroxy Acids (P.H.A.) with Gluconolactone.

The commonality among these various acids is their keratolytic action, meaning they eliminate dead cells on the skin's surface. This is referred to aschemical exfoliation. Indeed, even though there is a natural process of cell renewal (desquamation), it can be slowed down by various causes. However, two main factors slow down cell renewal: age and excess sebum. A slowdown in cell renewal can lead to various skin discomforts such as the appearance of imperfections, dull complexion, or the accelerated appearance of signs of aging.

Therefore, it is essential to support the cellular renewal process, particularly with the help of cosmetics containing keratolytic active ingredients such as fruit acids. However, it is important to choose the right acid based on your skin type.

Dry skin is a skin type characterized by tightness and irritation across the entire face. These symptoms are caused by an abnormality in the skin barrier. The use of potent keratolytic agents on dry skin can exacerbate irritations and further thin the skin barrier. This is the case, for example, with glycolic acid , which is an A.H.A. Indeed, it is an excellent keratolytic agent well known for combating imperfections and signs of aging. However, due to its low molecular weight, it penetrates deeply into the epidermis and can cause skin irritations.

Thus, if you have dry skin, it is advisable to lean towards lactic acid, which is known for being a gentle exfoliant. Due to its larger molecular weight compared to glycolic acid, the lactic acid remains on the skin's surface. This superficial action allows it to exfoliate the skin without causing irritation. Moreover, scientific studies have proven that the application of 5% lactic acid increases skin hydration. Indeed, lactic acid has the ability to retain water molecules within the epidermis, thereby limiting the phenomenon of insensible water loss. Additionally, it is a molecule naturally present in the skin as it is part of the Natural Moisturizing Factor (NMF). In fact, its natural presence in the skin contributes to its gentler effect on the skin.

Note: The NMF (or Natural Moisturizing Factor) represents 30% of the total dry weight of the stratum corneum. It is composed of amino acids, their derivatives, and extracellular compounds such as lactic acid or urea. Its hygroscopic properties allow it to capture and retain water in the stratum corneum, thus maintaining good skin hydration.

Thus, lactic acid is a gentle exfoliant ideal for dry skin. It helps to remove dead cells, revealing smoother and brighter skin, while maintaining good skin hydration.