THE DIFFERENCE BETWEEN GLYCOLIC AND SALICYLIC ACID 

Chemical exfoliants are a diverse group of skin care actives that can be used to target anything from dull skin to clogged pores and wrinkles.There are two main classes of chemical exfoliants: alpha hydroxy acids (AHAs) and beta hydroxy acids (BHAs). Don’t let the term acid scare you. The skin barrier is naturally acidic and at the concentrations available to consumers, these products are safe and excellent additions to a skin care routine [1].Two specific examples of AHAs and BHAs are glycolic and salicylic acid, respectively. Below, we explore the differences between these two actives and discuss how to incorporate them into your skincare routine. 

ALPHA HYDROXY ACIDS

AHAs are weak organic acids that are found naturally occurring in many foods including sugarcane, milk, and most fruits. Structurally, AHAs have one hydroxyl group attached to the α-position of the carboxyl group, making them water soluble [2]. Dermatologists have used them in higher concentrations to accomplish superficial and medium-depth chemical peels as they have profound effects on the skin keratinization process [3].AHAs disrupt the cohesion of corneocytes at the skin barrier, stimulating cell turnover and skin renewal. Glycolic acid specifically has been used to treat acne, decrease epidermal thickness, increase cellular turnover rates, and increase collagen production [4]. These effects are most observed when glycolic acid is used consistently at significantly lower concentrations than what would be used in a chemical peel (8-25%) to avoid possible irritation. While glycolic acid is excellent at reducing signs of photoaging, high concentrations mixed with too much sun exposure may exacerbate skin problems [3]. 

SALICYLIC ACID 

Salicylic acid is commonly categorized as a BHAhowever, it has a unique structure that puts it in a class of its own [5]. Because salicylic acid has both the carboxyland hydroxyl group attached to a benzene ring, this compoundis actually more acidic than other hydroxy acids and has lipophilic properties.This is why salicylic acid is used in much lower concentrations (0.5-10%) and is so effective at fighting acne; it is better at penetrating the oily sebaceous glands where acne originates [6].While salicylic acid also increases new skin cell turnover, it works via a different mechanism than AHAs. Instead of breaking down keratin (keratinolytic activity), salicylic acid disrupts protein complexes called desmosomes which areresponsible with the tight linking of the keratinocytes that form the outermost layer of the skin barrier(desmolytic activity) [7]. Salicylic acid is chemically related to acetylsalicylic acid (aspirin) and thus, benefits acne via its anti-inflammatory properties [8]. 

HYDROXY ACIDS IN SKIN CARE 

Glycolic and salicylic acid can safely be used in tandem as regular components of a skin care routine to improve hyperpigmentation and reduce inflammation. It is recommended to start at lower concentrations and increase as necessary, always wearing sunscreen when you do incorporate these ingredients as they can increase skin sensitivity to the sun [9]. If you’re interested in a chemical peel, the dermatologist will be able to guide you in understanding the subtle differences in choosing the right acid [10]. Salicylic acid peels are typically reserved for people with oily or acne-prone skin who may even have active acne while a glycolic acid peel is chosen when the major concerns are photoaging and hyperpigmentation without active acne [11]. 

Sources:

1. Proksch E (2018) pH in nature, humans and skin.J Dermatol 45, 1044–1052.

2. Kornhauser A, Coelho SG, Hearing VJ (2010) Applications of hydroxy acids: classification, mechanisms, and photoactivity.Clin Cosmet Investig Dermatol 3, 135–142.

3.  Tang S-C, Yang J-H (2018) Dual Effects of Alpha-Hydroxy Acids on the Skin.Molecules 23, 863.

4. Narda M, Trullas C, Brown A, Piquero-Casals J, Granger C, Fabbrocini G (2021) Glycolic acid adjusted to pH 4 stimulates collagen production and epidermal renewal without affecting levels of proinflammatory TNF-alpha in human skin explants.Journal of Cosmetic Dermatology 20, 513–521.

5. Zeichner JA (2016) The Use of Lipohydroxy Acid in Skin Care and Acne Treatment.J Clin Aesthet Dermatol 9, 40–43.

6. Arif T (2015) Salicylic acid as a peeling agent: a comprehensive review.Clin Cosmet Investig Dermatol 8, 455–461.

7. Samargandy S, Raggio BS (2021) Skin Resurfacing Chemical Peels. InStatPearls StatPearls Publishing, Treasure Island (FL).

8. Lu J, Cong T, Wen X, Li X, Du D, He G, Jiang X (2019) Salicylic acid treats acne vulgaris by suppressing AMPK/SREBP1 pathway in sebocytes.Experimental Dermatology 28, 786–794.

9. U.S. Food and Drug Administration, Guidance for Industry: Labeling for Cosmetics Containing Alpha Hydroxy Acids, Last updated April 20, 2021, Accessed on April 20, 2021.

10. Abdel-Motaleb AA, Abu-Dief EE, Hussein MR (2017) Dermal morphological changes following salicylic acid peeling and microdermabrasion.J Cosmet Dermatol 16, e9–e14.