Salicylic acid is a benchmark in cosmetics in the category of "exfoliants". Psoriasis, blackheads, dull complexion, brown spots, pimples, keratosis pilaris... it is used in a wide variety of skin disorders related to desquamation and hyperkeratosis of the stratum corneum. However, with this broad usage and high clinical efficacy, how does salicylic acid exert its "peeling effect" on the skin?
Salicylic acid, an exfoliating agent?
Well tolerated by all skin types, salicylic acid is classified as a β-hydroxy acid (BHA), although some categorize it as a phenolic aromatic acid. For several years, it has been used as an chemical peeling agent in dermatological practice for a number of cosmetic indications, primarily to improve the appearance and texture of rough and bumpy skin, prevent the formation of comedones, reduce pore obstructions, and even out skin tone. These characteristics are attributed to its mild exfoliating properties which cause the shedding of the skin's superficial layers followed by the regeneration of new epidermal tissues, leaving the skin softer, more uniform, and visibly smoother.
How does salicylic acid aid in exfoliation?
Several histological examinations have revealed that the topical application of a salicylic acid-based preparation has led to a dose-dependent thinning of the corneal layer in the tested samples compared to the controls, while causing no qualitative or quantitative changes in the epidermal structure and no effect on the mitotic activity of normal epidermis. It is then suggested that salicylic acid induces a slightly faster and easier loosening and detachment of groups of corneocytes by dissolving the intercellular cement, followed by an activation of the basal cells of the epidermis and the underlying fibroblasts.
Indeed, this desmolytic effect rather than keratolytic would be primarily explained by a decrease in a certain way of the cohesion between the corneocytes, without impacting the cell walls. It was discovered that salicylic acid works by disrupting cellular junctions (desmosomes), rather than breaking or lysing the intercellular keratin filaments. Thus, this acid is capable of breaking down and removing corneal cells by disrupting the connections between cells, without directly "injuring" the skin.
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