How to use lactic acid?

Thelactic acid is found in many cosmetic formulations under the INCI name "Lactic Acid". It is an organic acid from the family of alpha-hydroxy acids (A.H.A.) just like glycolic acid for example. It is naturally found in milk (from where it was first extracted), certain fruits and vegetables, and wine. It is also present in the human body. Indeed, it is involved in numerous biochemical processes and is part of the Natural Moisturising Factor (NMF).

Please note: the NMF or Natural Moisturising Factor accounts for 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.

Lactic acid can be used for various skin issues due to its multiple benefits and high tolerance:

• For skin with blemishes (blackheads, acne, scars and acne spots...) and a dull complexion :

Although acne is a multifactorial inflammatory disease, hyperseborrhea (excessive sebum production) is one of the major factors. Indeed, sebum provides a nutritious environment conducive to the growth of the bacteria responsible for acne, Cutibacterium acnes. Furthermore, an excess of sebum slows down the natural skin renewal process (desquamation). Therefore, sebum tends to clog the skin's pores, which promotes the appearance of imperfections.

Lactic acid, due to its keratolytic properties, stimulates cellular renewal by eliminating dead cells on the surface of the epidermis. This gentle chemical exfoliation helps to remove imperfections and revitalises the complexion's radiance.

A scientific study has proven that the application of products containing 2% lactic acid twice daily for 12 weeks reduces comedones by 56%.

Please note : in the case of acne, chemical exfoliation using fruit acids is the preferred method. Indeed, physical exfoliation can create micro-lesions in the skin, leading to an exacerbation of inflammation.

• To prevent wrinkles and reduce their appearance :

It is at the level of the dermis that new skin cells multiply in order to replace those that are eliminated. Furthermore, the dermis contains the fibroblasts which synthesise collagen fibres, elastin and hyaluronic acid, responsible for the density, elasticity and firmness of the skin.

However, with age, the structure of these fibroblasts changes. They can no longer synthesise collagen and elastin fibres, as well as hyaluronic acid. Thus, the first signs of ageing appear with a skin that becomes lax, a dilation of the pores, the wrinkles, as well as spots or even, the increase in dryness.

Lactic acid is a key active ingredient that combats signs of ageing. Possessing a higher molecular weight than glycolic acid, it penetrates the epidermis less deeply. Although it acts on the surface, lactic acid has the ability to indirectly increase the synthesis of collagen and elastin fibres. Indeed, under physiological conditions (in an aqueous environment), lactic acid transforms into pyruvic acid through a deprotonation reaction (loss of a hydrogen atom). Pyruvic acid, being more lipophilic, penetrates the epidermis more easily. It thus stimulates the synthesis of collagen and elastin fibres by fibroblasts. The skin gains in elasticity, density, and firmness.

Furthermore, lactic acid, which is part of the NMF (Natural Moisturising Factor), helps to maintain good hydration of the stratum corneum due to its hygroscopic properties. Adequate skin hydration strengthens the skin's barrier function and helps to prevent the appearance of dehydration wrinkles.

• Fading pigmentation spots :

Brown spots are caused by a localised overproduction of melanin, the pigment responsible for the natural colouration of the skin. They vary in size and affect the uniformity of the complexion. They can cause some discomfort in the daily lives of those affected.

Scientific studies have also highlighted the depigmenting properties of lactic acid. Indeed, lactic acid inhibits the activity of enzymes involved in the process of melanogenesis (the mechanism responsible for the production of melanin): the tyrosinases. The results of the studies prove that the topical application of lactic acid significantly reduces pigmentation spots. However, these studies were conducted using a peel with 82% lactic acid (this is above the concentration allowed in cosmetics, which is 10%). The use of high-dose lactic acid requires the intervention of a healthcare professional.

Take note : Lactic acid is also used in cosmetics as it is a pH regulator.

In cosmetics, lactic acid is used in serums, creams, lotions, and cleansers to make the skin smoother and more radiant. According to European regulations, it is permitted at a maximum concentration of 10% in cosmetic products. The effectiveness of a lactic acid treatment depends on its concentration and pH. The higher the concentration and the lower the pH, the better the action of the lactic acid will be.

A lactic acid treatment should be applied to theentire face. You can also apply it to the neck to prevent the appearance of wrinkles or brown spots in that area.

Lactic acid is a photosensitising molecule meaning that it increases the skin's sensitivity to the sun (risk of skin irritation and sunburn). Therefore, use your lactic acid skincare only in the evening. A broad-spectrum sun protection should be applied the following morning.

Lactic acid is a mild acid generally well tolerated by all skin types. However, before using a product containing it, perform a skin tolerance test by applying a few drops of the product to the crook of your arm. If you observe a skin reaction, do not use your product on the face.

The peeling serum is suitable for all skin types, even the most sensitive. It is particularly recommended for blemished skin and dull complexions. Based on 10% lactic acid and acerola extract , it eliminates dead cells revealing smoother and brighter skin. Apply 3 to 4 drops of your lactic acid serum to the face, only in the evening. We recommend using your serum for a period of at least 4 weeks in order to observe its effects.

Please note : initial uses may cause slight redness. This is simply the time needed for the skin to become accustomed to the molecule. These effects will fade after several uses.

The peeling mask is suitable for all skin types, however, its use is not recommended for sensitive skin due to its high concentration of A.H.A. Composed of an exfoliating complex, it unclogs pores and refines skin texture. This gel mask should be applied once or twice a week on clean, dry skin, in the evening only. It leaves the complexion unified and the skin texture smoothed.

Ensure not to use these treatments in the morning and limit any sun exposure for a week after application. The use of a broad-spectrum sunscreen is also highly recommended.

• Rotsztejn H. & al. Lactic and lactobionic acids as typically moisturising compounds. International Journal of Dermatology (2018)