Alpha hydroxy acids (AHAs) are naturally occurring compounds found in many foods, including glycolic acid (sugar cane), lactic acid (milk), citric acid (citrus fruits), and malic acid (apples) among others. The most commonly used alpha-hydroxy acids are glycolic and lactic acids.
AHA's act as an exfoliant, resulting in the sloughing off of dull, rough skin and promoting cellular renewal. AHAs were found to promote softer, smoother skin, fade wrinkles, lighten age spots, and decrease blemishes. Further studies have shown AHAs to increase epidermal proliferation and thickness, and restore hydration and plumpness through an increase in hyaluronic acid.
Alpha Hydroxy Acids are also able to travel deeper into the dermis where they are shown to effectively reverse the signs of photo aging.
Research has found AHAs to improve the quality of elastic fibers, increase collagen density, and increase dermal thickness.
They also promote increased gene expression of collagen and hyaluronic acid in the dermis. These effects result in a significant improvement in wrinkles, skin hydration, and dermal characteristics such as skin elasticity and tone.
A an early study reported 4 weeks of treatment of 12% lactic acid resulted in a 19% increase in epidermal thickness and increased amounts of collagen in the dermis. Other colleagues comparing 25% glycolic acid treatment for 6 months reported a 25% improvement in skin thickness, and significant dermal changes with increased collagen density and elastin quality.
Concentration of AHAs is an important element for results. Exfoliation is directly proportional to the duration of application, and higher concentrations of acids have more potent anti-aging effects.
A study comparing 5% versus 12% lactic acid found that while 5% effectively causes epidermal changes it did not reach the dermis, whereas the 12% solution was found to influence both the epidermis and the dermis. A study using slightly lower (8% glycolic acid) revealed a significant number of patients with improvement of some aspect of photo aging, demonstrated by decreasing sallowness, hyper-pigmentation, and roughness.
Higher concentrations of AHAs, though more active, can have an irritating effect on the skin causing redness and inflammation. Newer formulations combine glycolic acid with an amino acid such as arginine and form a time-release system that reduces the risk of irritation without affecting glycolic acid efficacy.
The FDA has established that AHAs are safe in cosmetic products at concentrations of 10% or less. They are also formulated to reduce the skin's sensitivity to the sun or accompanied by directions to use sun protection daily.
Stronger formulations of AHAs (concentrations up to 30% or more) are safe if applied only by trained professionals. Such use should be brief and followed by thorough rinsing. Sun protection should be used daily.
It is not just the percentage of AHAs that are important, but also the pH of the formulation. AHAs are more bioavailable and work best at their native lower pH. For daily products (10% or less) optimal pH should be around 3.5- 4.0.