Alpha hydroxy acid (AHA)

Alpha hydroxyl acids are group of structurally related organic acids found in natural sources or synthesized in the laboratory. The action of AHAs are not well understood, also some researcher have concluded that they causes skin thickness, improvement in skin elasticity and increased collagen content, other researcher are concerned about the end result of constant low-grade irritation and the potential to produce reactive free radicals that are capable of damaging collagen and elastic fibers. The effectiveness of an AHA skin care products depends mainly of the concentration of AHAS rather than accompanying inactive ingredient. Products with AHAs concentration below 8% appear to be of no benefit. Most studies of 8-15% alpha hydroxyl acid report very modest improvements in wrinkle and skin smoothness. Concentration at the high end of this range might be a little bit more effective but are more likely cause irritation.


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, French women in the court of Louis XIV washed their faces with old wine and some people were applying old fashioned facial masks made from fruit, honey or yogurt.
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.


Chemistry of alpha hydroxy acid
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:Glycolic Acid (CH2OH-COOH) Lactic Acid (CH3-CHOH-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. 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.

Mechanism
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 humectants that absorbs moisture from the atmosphere. Second AHAs increase exfoliation and skin cell turnover. 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, 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.