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Hydroxy
acids are naturally occurring acids, derived from the sugars
in particular plants. Some examples are Lactic Acid (Milk),
Tartaric Acid (Grapes), Citric Acid (Citrus Fruits), Malic
Acid (Apples), Glycolic Acid (Sugar Cane), and Mandelic
Acid (Bitter Almonds). These acids were able to improve
the skin because they had molecules small enough to penetrate
the outer (corneum statum) layer of the skin, and reach
the lower (dermis) layer.
Hydroxy
acids are organic carboxylic acids classified into alpha
hydroxy acids (AHAs) and beta hydroxy acids (BHAs) according
to their molecular structure.
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AHAs
range from simple aliphatic compounds to complex molecules.
Many are derived from natural sources and are often referred
to as fruit acids. The different AHAs include the following:
glycolic acid, lactic acid, citric acid, mandelic acid, malic
acid, and tartaric acid.
BHAs
are aromatic compounds. Salicylic acid is the reference BHA;
it has dermolytic properties and helps in various skin disorders.
Other BHAs include 2-hydroxy-5-octanoyl benzoic acid.
They work by dissolving the cement that holds dead skin cells
together, increasing cell turnover, and sloughing off dull,
rough skin on the surface. The skin appears smoother and more
uniform. The likely cause of these changes is the property
of AHAs to enhance epidermal shedding. Another added benefit
of alpha hydroxy acids is the way they can improve the skin's
ability to retain moisture. Most of the skin's moisture is
lost through the cracks of the dead skin cells on the outer
layer. By removing the dead skin, water can not be easily
lost through the cracks.
Despite
their popularity, the exact mechanisms of action of hydroxy
acids remain largely controversial; however, at least one
aspect of its biological activities may be attributed to the
inherent acid strength of the compounds. Studies show that
AHAs may increase sensitivity to UV radiation and that sunscreen
application would be advisable when using these products.
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