Skin Resurfacing With Alpha Hydroxy Acids
Alpha Hydroxy Acids are naturally occurring compounds derived from the natural sugars of particular biological sources (usually fruits). They are named as such because alpha hydroxy acids are a class of chemical compounds that consist of a carboxylic acid substituted with a hydroxy group on the adjacent carbon. They may be either naturally occurring or synthetic, though for use in skincare studies have demonstrated that naturally derived hydroxy acids are up to four times gentler on the skin than their more irritating synthetic versions. Therefore, only fruit-derived hydroxy acids are recommended and discussed here.
These acids work at the very base of the stratum corneum in the epidermis (i.e. the top layer of skin) to dissolve the “cement” that holds dead skin cells together. This increases cell turnover and influences the structure of the new stratum corneum being made. The result is skin that is more flexible, smoother, and more even in tone/pigmentation. At greater concentrations deeper structural effects occur, including the stimulation of higher amounts of mucopolysaccharides (natural skin moisturizing compounds) and collagen production which leads to an increase in skin thickness and firmness. Eventually, after weeks of daily application, these hydroxy acids can condition skin to look softer, smoother, less wrinkled, and progressively more even in tone.
Natural sources of hydroxy acids include glycolic acid from sugarcane, lactic acid from sour milk or bilberry fruit, malic acid from apples or maple tree sap, citric acid from citrus fruits, and tartaric acid from grapes. In ancient Egyptian texts it has been written that Cleopatra would wash her face with sour milk, an early antecedent of today's lactic acid treatments. While all of these hydroxy acids perform unique functions on the skin and work in concert to bring about controlled epidermal renewal, glycolic acid is a somewhat bigger superstar in the group. This is because glycolic acid has the smallest molecular size of any of these hydroxy acids and is therefore able to penetrate the deepest to have more dramatic effects at lower skin levels.
In low concentrations glycolic acid reduces cell adhesion in the top layer of the skin to promote exfoliation of the epidermis to give the skin a smoother texture with continual use. This relatively low concentration lends itself to daily use for controlling acne and fine lines as well as lessening the appearance of hyperpigmentation (age spots, freckles, etc). More advanced formulations use a higher percentage of glycolic acid in concert with the other aforementioned alpha hydroxy acids to accelerate these results and make them more dramatic. Not only do higher concentrations of hydroxy acids have a greater resurfacing effect in skincare products but they can also stimulate collagen synthesis at just below the clinical level (clinical concentrations are usually at 15% or more and are only appropriate for professionally-applied face peels). When obtained from natural sources even those with sensitive skin should not experience irritation at concentrations under 15%.
Ensuring Hydroxy Acid Formula Effectiveness
It is important to note that in addition to the concentration of hydroxy acids in products there are other factors that contribute or detract from their effectiveness. One of the most important factors in the effectiveness of hydroxy acid containing products is the pH level of the formula. An ideal pH is 3.5 to 4.0 (any lower and the product may be too acidic while any higher and the product's exfoliating benefits may be nullified). In the case of the undereye area, more is not always better. This fragile skin region is very sensitive and hydroxy acids should be used in low concentrations (the face is very forgiving of aggressive treatments, while the undereye area is not). Those using Retin-A, Renova, Accutane, or anything else that already has exfoliating or skin compromising actions should not use hydroxy acid products unless your physician has recommended that you do so. Even though at appropriate concentrations hydroxy acids should not overly increase sun sensitivity, using a product containing sunscreen during the day to protect the skin from UV exposure is recommended (which is beneficial even when not using hydroxy acids).