浓度低于3%、酸硷度高于3.5时，主要为加强保溼效果，当浓度大于6%、酸硷度低于3.5时，对于粉刺痘痘的调理才较为有效，浓度越高效果越强，但刺激性也越大[2]。
[2] 邱品齐，「认识你所不知道的药妆品：皮肤科医师特选篇」，大境，2010/03/18。
在黑色素合成之后，加速皮肤更新
Reference：药妆品学 Cosmeceuticals, 2nd edition
【Glycolic Acid】
Rating: BEST
Benefits: Anti-Aging, Evens Skin Tone, Smooths Bumpy Skin
Categories: Exfoliant, Humectant, pH Adjuster/Stabilizer
＊ The most-researched AHA (alpha hydroxy acid) with a long history of safe use
＊ Helps renew skin’s surface, visibly improving several signs of aging
＊ Significantly increases skin’s hydration
＊ New research shows it may protect skin from UV damage
Glycolic acid is a type of alpha hydroxy acid (AHA) that, like other ingredients in the category, can act as a water-binding agent and, when properly formulated and used in concentrations of 5% or greater, as an exfoliant. While there are several other types of AHA, glycolic acid is by far the one with the most research backing its effectiveness.
In its capacity as an exfoliant, it can help shed dead skin to renew skin’s surface, which results in the improvement of several signs of aging, including sun damage, uneven tone, rough, flaky patches of skin, fine lines, and wrinkles. These benefits are obtainable by choosing a leave-on AHA exfoliant that contains 5–10% glycolic acid when it is used as the sole exfoliating acid. It must also be formulated at a pH between 3-4, which is where optimal exfoliation occurs.
Studies also show that glycolic acid significantly increases skin’s hydration. It does this by helping skin make substances like mucopolysaccharides, which aid hydration by increasing skin’s natural content of hyaluronic acid, which in turn enhances resilience and improves texture.
One exciting new note about glycolic acid: emerging research shows it might even protect skin against UV damage (in addition to reducing its damaging after-effects), though more studies need to be done (and of course it doesn’t replace the need for sunscreen). It’s worth noting that most AHA products do carry a warning about unprotected sun exposure, since the manner in which AHAs exfoliate reveals fresh new skin that can be more susceptible to sun damage.
Glycolic acid occurs naturally in sugar cane, but is most effective when synthesized in a lab, where its potency and concentration are optimized for use in skin care. Using plant sugars, like sugar maple, for their glycolic acid content is an option, but the bulk of the reimized for effectiveness, purity, stability, and pH, all critical to getting effective glycolic acid products.
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