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What are the Differences Between Alpha Hydroxy Acids and Beta Hydroxy Acids?

The chemical structures of Salicylic Acid (BHA) and Alpha Hydroxy Acids (AHA) are very different from each other. While Alpha Hydroxy Acids are soluble in water, Salicylic Acid is soluble in lipids. Although both belong to the Hydroxy Acid family, they act on different layers of the skin. Salicylic Acid acts on the upper epidermis, while AHAs are believed to penetrate into the dermis [1, 2]. Another difference between AHAs and BHAs is that AHAs can cause some stinging and tingling or slight redness on the skin depending on the usage dose and the time they are kept on the skin. Such situations are not encountered with BHAs (salicylic acid).

Because of their lipophilic (fat-soluble) structure, BHAs have the ability to penetrate the sebaceous material in the follicles and exfoliate the pores [3]. The comedolytic structures of BHAs were proven by Kligman A. In the study, the number of microcomedones in a person treated with 2% salicylic acid and the number of microcomedones in a person treated with 8% glycolic acid were compared and examined by observing. According to the results obtained from the study, while the number and density of microcomedones in the person receiving the formulation containing glycolic acid did not show any change, the results in the person receiving the formulation containing BHA were significantly reduced [4].

Due to its anti-inflammatory properties, products containing salicylic acid are preferred for acne or acne-prone skin. In a clinical study conducted by Di Nardo in 1995, it was concluded that products consisting of a combination of Glycolic and Salicylic Acid are more effective than benzoyl peroxide in preventing inflammation in acne lesions [5]. In addition, when the products formulated with the combination of AHA-BHA and the products formulated with only BHA (Salicylic Acid) were compared, it was revealed that the combined use of AHA and BHA was much more effective in the improvement of acne lesions than the results obtained with the use of salicylic acid alone.

It has also been reported in studies that Salicylic Acid is more effective than AHAs in cases of rosacea, due to its anti-inflammatory properties.

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  1. Draelos Z. Hydroxy acide for the treatment of aging skin. J Geriatric Dermatol. 1997;5:236.
  2. Brackett W. The chemistry of salicylic acid. Cosmet Dermatol. 1997;10(suppl):5.
  3. Davies M, Marks R. Studies on the effect of salicylic acid on normal skin. Br J Dermatol. 1976;95:187.
  4. Kligman A. A comparative evaluation of a novel low-strength salicylic acid cream and glycolic acid. Products on human skin. Cosmet Dermatol. 1997;10 (suppl):S11.
  5. Di Nardo J. A comparison of salicylic acid, salicylic acid with glycolic acid and benzoyl peroxide in the treatment of acne. Cosmet Dermatol. 1995;8:43-44,14.