Natural chemical, used in skin exfoliation. Glycolic acid is one of several alpha hydroxy acids commonly used in the skincare industry. Alpha hydroxy acids are weak acids, i.e., weakly ionized. In skincare, they are used as exfoliants because they are safe to use at relatively high concentrations. Although alpha hydroxy acids are present in fruits and milk, these days, the acids are likely to be obtained by bacterial fermentation. As far as exfoliation power and relative safety are concerned, what matters is the final pH, which is determined by the molar concentration and the tendency of the acid to dissociate, measured by the pK. There are no particular benefits to one or another acid despite claims like “better penetration” for glycolic acid. Many products advertising high concentrations of acids have been buffered using a base like potassium or sodium hydroxide (KOH or NaOH) so that most of the acid is gone and what is left is mostly salt. The exfoliation power will be significantly diminished. Exfoliation increases sensitivity to UV. Prevent exposure of your skin to the sun after exfoliation.