Why Choose Glycolic Acid?
There is a normal turnover of cells with new cells replacing aging and dying cells. The dying and dead cells form the outermost layer of skin, which we call the "keratin layer". The keratin layer is an important consideration for a number of reasons:
Glycolic Peel can be performed on the face, neck, chest, hands and even the arms and legs. It uses a solution applied to the skin to remove dead skin cells and stimulate the production of new skin cells. The solution is applied to the skin and a burning sensation similar to a sunburn is usually noted by patients after the procedure. For deeper peels, some patients require anesthesia. Several chemical solutions exist that can peel away skin from the superficial, medium, or deep layers.
Long before the chemical structure, or even the existence, of alpha -hydroxy acids (AHA's) were known, they were unknowingly being used as an ingredient for improving the condition of skin. Egyptian women took baths in sour milk in order to improve their skin. French women in the court of Louis XIV washed their faces with old wine for the same reasons. Old fashioned facial masks made from fruit, honey or yogurt were also unknowingly taking advantage of AHAs as their active ingredients.
Alpha -hydroxy acids are commonly found and isolated from fruits of all sorts. That is why they are referred to as fruit acids. For example, malic acid is found in apples, citric acid can be isolated from most all citrus fruits and glycolic acid is commonly found in honey or sugar cane. Another source of AHAs is from the fermentation of natural products. Lactic acid is found in milk that has soured, and tartaric acid can be isolated from fermented grapes (wine). It is this natural, feel good origin of alpha -hydroxy acids that make them so appealing. Couple this with the genuine hi-tech biochemistry that they exhibit and it is no mystery as to why they are so popular today.
A Little Chemistry: Organic vs. Mineral Acids
Chemically speaking, an alpha -hydroxy acid is a low molecular weight organic acid. Most people associate the word "acid" with potent and dangerous acids like hydrochloric and sulfuric. These acids are called mineral acids and are indeed potent and dangerous. Most are strong enough to dissolve metals. An organic acid however, differs greatly from a mineral acid. Organic acids are much, much milder than mineral acids and occur quite commonly in everyday life. Acetic acid, for example, is the organic acid that gives vinegar its characteristic sour taste.
An organic acid is chemically defined as a molecule that possesses a carboxylic acid (-COOH) group:
Acetic Acid (CH3-COOH); Glycolic Acid (CH2OH-COOH) Lactic Acid (CH3-CHOH-COOH) Beta Hydroxy Acid (CH2OH-CH2-COOH)
An AHA such as glycolic or lactic acid has a hydroxyl group (-OH) present on the carbon atom immediately adjacent to the acid group. This position is defined as "alpha " (first letter of the Greek alphabet) because it is the first carbon next to the acid group. Beta -hydroxy acids are thus molecules where the hydroxy group is on the second carbon next to the acid group. Glycolic Acid is the most commonly used AHA. Because of its small molecular weight and size, it is presumed to have a better capacity to penetrate skin. Lactic acid on the other hand, has a larger molecular weight than glycolic acid but is capable of being converted in vivo to pyruvic acid (an alpha keto acid) which is presumed to be a more effective exfoliating agent. It should be noted that neither salicylic acid nor retinoic acid are alpha -hydroxy acids.
Today, alpha -hydroxy acids are used extensively in cosmetic dermatology. At concentrations lower than 10%, they are regularly formulated into everyday use creams. At these levels, skin benefits result from continuous use and result in a gradual reduction in fine lines and an overall improvement in skin texture brought about by accelerated desquamation
(exfoliation). At higher concentrations, AHAs function as peeling agents which act more rapidly and at a deeper level. Glycolic acid peels at concentrations of 20-70% are commonly used by dermatologists and plastic surgeons to remove severe acne scarring and skin pigmentation irregularities. Their effectiveness depends on the contact time of the acid and the number of peeling sessions. Milder peels (10-40%) can be carried out in skin care salons. Peels, in general, are being used more frequently to treat the wrinkles and skin discoloration resulting from solar damaged skin (actinic aging). They are also finding more and more use as anti-aging ingredients to combat the loss of smoothness and skin elasticity associated with chronological aging. The war against wrinkles seems to be never ending.
The full mechanism of action of alpha -hydroxy acids is not yet fully understood. It is known however, that they function in two distinct fashions: First, they can act as a simple humectant that absorbs moisture from the atmosphere. When applied to the skin, these hydrated AHAs act to increase the water content of the skin and thus moisturize the outer layer of the epidermis (the stratum corneum) and consequently make the skin softer and more flexible. The second method by which AHAs are thought to act is by reducing corneocyte adhesion and accelerating cell proliferation within the deeper basal layer of the skin. This exfoliating action of AHAs occurs as a result of their ability to break the bonds between dead skin cells that form at the surface of the skin. Skin normally has a dead layer of cells at its surface (the corneocyte layer), and AHAs can speed up the normal process of skin cell regeneration and sloughing. This results in increased flexibility of the skin as well as decreased formation of large dry skin flakes at the surface of the skin. When applied in the high concentrations of a peel, AHA's operate at a deeper level and cause detachment of keratinocytes and epidermolysis. At lower concentrations, AHAs primarily reduce intercorneocyte cohesion thus promoting exfoliation and thinning of the stratum corneum. A thinner stratum corneum is more compact and flexible.
Sun damaged skin is becoming more and more of a problem in our society. Prematurely aged skin brought about by long term UV radiation exposure (actinic aging), is in part caused by a thickening of the stratum corneum resulting from increased corneocyte cohesion. Long term UV radiation exposure also degrades collagen in the dermis layer of the skin. There is also evidence that excessive amounts of abnormal elastic fibers also tend to accumulate within the dermis of photodamaged skin. Glycolic acid at low concentrations works well to decrease corneocyte cohesion by promoting exfoliation of the outer layers of the stratum corneum. This is especially relevant since most pigmentation alterations associated with photodamage can be attributed to the thickening of the stratum corneum.
Most of the evidence on how AHAs work seems to point to exfoliation and the resulting turnover of new cells in the outer epidermal layer of the skin. There is increasing evidence however, that AHAs may be working at a much deeper level. There may well be increases in procollagen and Type I collagen that occur in the deeper dermis layer brought about by long term treatment with AHAs. One interesting study showed that topical treatment twice a day for 3 months with a 5% glycolic acid cream, at pH 2.8, affected surface and epidermal changes, while the same treatment, but with a 12% cream, reached deeper and influenced both the epidermis and the deeper dermis layer, and resulted in increased epidermal and dermal firmness and thickness. Both showed clinical improvement in skin smoothness and in the appearance of lines and wrinkles. Another interesting study showed that AHAs may thin the outer stratum corneum, but actually end up increasing the overall thickness of the epidermis. This thickening is accompanied by increased synthesis of glycosaminoglycans and collagen. It is becoming apparent that alpha -hydroxy acids may do more than just increase exfoliation and skin cell turnover.