Lactic acid, a natural organic acid, is a type of alpha-hydroxy acid (AHA) and a major component of the natural moisturizing factor (NMF) of the human epidermis.

Source
Currently, lactic acid is mainly obtained by chemical synthesis.

Purposes
In the cosmetics industry, it is mainly used as a moisturizer and exfoliator.

Efficacy
Studies have shown that lactic acid has the following efficacy[1-2]:

? Anti-aging: it promotes skin firmness and fullness and reduces the appearance of fine lines and wrinkles.

? Keratin exfoliation: it accelerates the renewal of epidermis, improves skin pigmentation to a certain extent, and makes skin tone more even.

?  It can be used as a moisturizer to increase the water content of the skin.

?  Lactic acid is also commonly used as a pH adjuster.

Applications
It is commonly used in cleansing and renewing products as it can adjust pH and promote exfoliation.

It is recommended to use the product according to the instructions on the packaging, e.g. using it together with sunscreen cosmetics.

References
[1] Xu DT. Cosmeceuticals, 3rd edition [M]. Beijing: People's Medical Publishing House, 2018.05

[2] Wu HH. The development status and applied research of the lactic acid and its derivatives in the domestic and overseas. J Northwest Univ National: Nat sci, 2010, 31 (2): 67-70 (in Chinese).

Salicylic acid is a representative type of β-hydroxy acid (BHA), which is fat-soluble and highly permeable.

Source
It is found in the bark of willow trees in nature. Currently, salicylic acid is mainly obtained by chemical synthesis.

Purposes
In the cosmetic industry, it is commonly used in exfoliation and pore-clearing products; in the pharmaceutical field, it is often used to treat acne, seborrheic dermatitis, etc.

Efficacy
The efficacy of salicylic acid in cosmetic applications[1-4]:

? Pore-clearing

Thanks to its lipolytic properties, salicylic acid can penetrate into the stratum corneum and pores, facilitating the dissolution of old keratin in pores and unclogging pores.

?  Keratin exfoliator

It can play a solubilizing role by acting on the intercellular adhesion of cells, reducing the adhesion of keratinocytes and promoting keratin renewal.

Applications
It is often used as a skin conditioning agent in pimple and acne removal and pore cleansing products.

References
[1] Peng R, Tian LX, Ci X. Advances in the application of supramolecular salicylic acid in skin cosmetology[J]. Journal of Modern Medicine & Health, 2019, 35(14):4. Journal of Shihezi University (Natural Science), 2003, 7(4):3 (in Chinese).

[2] Anonymous. Dermal pharmacology of salicylic acid [J]. International Journal of Dermatology and Venereology, 1977, Vol. 3, No. 4, pp. 242-243, ISTIC, 2020.

[3] Ling Z. Keratin conditioner - salicylic acid [J]. Medical Aesthetics and Cosmetology, 2004, 000(006):107-108 (in Chinese).

[4] Shan OQ, Tian HM, You Y. The latest application and prospect of salicylic acid in medical cosmetology[J]. Medical Aesthetics and Beauty, 2019, v.28; No.267(03):175-177 (in Chinese).