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Hydroxy acids are chemical exfoliants. They have been found to increase the synthesis of collagen and elastic fibres, increase the thickness of the skins epidermal layer, help treat sun damage, increase
the skins cell turnover and the skins ability to retain water. The two main hydoxy acids are AHA's (alpha hydroxy acids) and BHA's (beta hydroxy acids).
Alpha hydroxy acids work on the skins epidermal surface whereas Beta hydroxy acids penetrate deeper into the skin.The pH of hydroxy acids can cause significant irritation to the skin. This is a problem because the pH ranges of hydroxy acids enchance the exfoliation characteristics of hydroxy acids.
The most commonly used BHA's and AHA's include:
1)Salicylic acid - BHA
Salicylic acid is the most commonly used (BHA). It is a non-abrasive exfoliant which has been shown to increase cell turnover and the production of skin cells and proteins. It is indicated for photoaging, acne, post inflammatory hyperpigmentation and melasma. It has also been reported to reduce sebum production. It works by unblocking pores and dissolving acne causing bacteria.
It is not fully understood how salicylic acid works. It has has been suggested that it weakens the bonds between corneocytes in the stratum corneum on the skin. This results in softening of the stratum corneum.
Do not use salicylic acid if you are allergic to aspirin.
2)Glycolic acid - AHA
Alpha hydroxy acids are also known as fruit acids because they are found in fruits such as lemons,grapes and apples.The mechanism of action of AHAs is not fully understood either however it is suggested that they work by removing calcium ions in the epidermal cells of the skin this results in removal of dead skin cells, increase in collagen and hyaluronic acid production as well as increased cell turnover and reduction in fine lines
Gycolic acid is a (AHA) alpha hydroxy acid. It is commonly used in concentrations of (2-5 %) as an exfoliant, It can also be used at higher concentrations as a skin peel under the supervision of a dermatologist. It has been shown to improve dry skin, sun damage, hyperpigmentantion and acne .It easily penetrates the skin because of the particle size.
Other common AHs include lactic acid and mandelic acid.
"Although salicylic acid and other hydroxy acids such as glycolic acid have been shown to be effective in treating photoaging and hyperpigmentation caused by sun UV exposure, they increase sensitivity to the sun. It is therefore important to use sun protection when using hydroxy acids".
References
Alpha Hydroxy Acids (AHAs): the chemist's viewpoint and the cosmetician's viewpoint. 1995. Cosmetics, 23(2), pp. 22.
- Fartasch, M., Teal, J., & Menon, G. K. (1997). Mode of action of glycolic acid on human stratum corneum: Ultrastructural and functional evaluation of the epidermal barrier. Archives of Dermatological Research, 289(7), 404-409. doi:10.1007/s004030050212
Tran, D., Townley, J. P., Barnes, T. M., & Greive, K. A. (2015). An antiaging skin care system containing alpha hydroxy acids and vitamins improves the biomechanical parameters of facial skin. Clinical, Cosmetic and Investigational Dermatology, 8, 9.
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