The dangers of lactic acid.

Belonging to the same family as theglycolic acid, lactic acid is part of the alpha-hydroxy acids. It is often used in peelings as it possesses excellent keratolytic properties, meaning it removes dead cells from the surface of the epidermis.

Indeed, it dissolves the intercellular bonds. By stimulating cellular renewal, it revives dull complexions and prevents the appearance of blemishes (spots, blackheads...). Compared to glycolic acid, lactic acid is better tolerated as it has a higher molecular weight allowing it to remain on the surface of the epidermis and be less irritating.

However, although it is suitable for all skin types, lactic acid remains a potent active ingredient that can cause side effects :

• An increase in sun sensitivity : Like all molecules in the A.H.A. family, lactic acid is a photosensitising molecule, meaning it increases the skin's sensitivity to the sun. Therefore, applying lactic acid followed by sun exposure can lead to sunburn or skin irritations ;

• Irritations: Although it is gentler than glycolic acid, lactic acid remains an acid. It can cause mild to moderate burning sensations that are temporary. However, these effects are rare because at a concentration of 10% or less (the concentration of lactic acid permitted in cosmetics), the use of lactic acid is safe.

Like other fruit acids, lactic acid does not mix well with the sun. Indeed, it increases the skin's sensitivity to the sun's UV rays and heightens the risk of sunburn, even without direct exposure.Due to its exfoliating power, the skin is left devoid of its natural protection against the sun's rays until the complete reformation of the stratum corneum, as well as the hydrolipidic film.

to apply your lactic acid treatments in the evening, especially as our cell renewal process is more active during the night. In the days following the application, remember to protect your skin from the sun by applying a broad-spectrum sun protection .

Furthermore, to avoid any undesirable effects, perform a skin tolerance test. Apply a few drops of your skincare product to the inside of your arm or the back of your hand and wait 24 hours. If your skin begins to sting and/or redden, reduce the acid concentration and/or space out the applications. Subsequently, you can gradually increase the frequency of application and the concentration.

• A.H.A. and B.H.A. : As a precautionary principle, we advise againstthe simultaneous use of lactic acid with other fruit acids, such as theglycolic acid and thesalicylic acid. Indeed, the application of an overly high concentration of keratolytic agents may sensitise the skin;

• Retinol This molecule is photosensitising and "potent". Moreover, it is a keratolytic agent. Therefore, it is not recommended to combine lactic acid with retinol as this could irritate the skin, especially in individuals with sensitive skin;

• Vitamin C : It is advised against combining Vitamin C with potent acids such as lactic acid. This mixture may cause irritations and inflammations at the epidermis level. However, it is possible to apply your lactic acid product in the evening and the one with Vitamin C in the morning.

• SMITH W. P. & co. Epidermal and dermal effects of topical lactic acid. Journal of the American Academy of Dermatology (1996).

• BERGFELD W. F. Cosmetic use of alpha-hydroxy acids. Current drug therapy (1997)

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