Lactic Acid

The most popular AHA in skincare and less irritating than glycolic acid. It can be naturally found in sour milk. It is a humectant moisturizing, pH stabilizing, and gently exfoliating ingredient, able to soften dry, cracked, and peeling skin.
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Lactic Acid

Overview

Lactic acid is the most used alpha-hydroxy acid (AHA) in skincare. It is a skin-identical ingredient, meaning that it is a part of the skin's Natural Moisturizing Factor (NMF) and it plays a role in balancing the microbiome and the pH of the skin’s surface. It can be naturally found in sour milk.

The addition of a small percentage of lactic acid to a skincare product is nothing but beneficial - it is a humectant moisturizing, pH stabilizing, and gently exfoliating ingredient, able to soften dry, cracked, and peeling skin.

In concentrations above 10%, lactic acid can be used as a chemical peel. These peels can remove the top layer of dead skin cells, stimulate skin renewal, and help to treat skin roughness and minor pigmentation issues.

The benefits of lactic acid for acne-prone skin are indisputable. At low concentrations, lactic acid is an adjuvant treatment that helps to maintain a healthy skin surface, while high concentration lactic acid peels may improve the appearance of acne scars.

When directly compared to glycolic acid, lactic acid has been found to be less irritating, more moisturizing, and just as effective at increasing the cell renewal rate.

There are two forms of lactic acid: L(+) form, which is found in the human body and produced by fermenting bacteria, and D(-) form, which is produced synthetically. L(+) form is generally less irritating and better tolerated, but in all other parameters, they are comparably effective. Glycolic acid may have some beneficial collagen-stimulating properties, but lactic acid is more suitable for dry and sensitive skin.

Lactic acid is also often compared to another AHA called mandelic acid, a large-molecule acid derived from almonds. Although they have very similar properties, mandelic acid differs in the fact that it offers additional antibacterial benefits and works even slower and gentler than lactic acid (due to its large molecule size).

Science

1
Tang, S. C., & Yang, J. H. (2018). Dual Effects of Alpha-Hydroxy Acids on the Skin. Molecules (Basel, Switzerland), 23(4), 863.
2
Huang, H. C., Lee, I. J., Huang, C., & Chang, T. M. (2020). Lactic Acid Bacteria and Lactic Acid for Skin Health and Melanogenesis Inhibition. Current pharmaceutical biotechnology, 21(7), 566–577.
3
Kontochristopoulos, G., & Platsidaki, E. (2017). Chemical peels in active acne and acne scars. Clinics in dermatology, 35(2), 179–182.
4
Smith, W.P. Comparative effectiveness of a-hydroxy acids on skin properties. International Journal of Cosmetic Science 18,7543 (1996)