What it is
Glycolic Acid is the smallest of the alpha hydroxy acids, with a low molecular weight that lets it penetrate readily and help loosen bonds between surface skin cells to encourage exfoliation. It is also used in formulas as a pH adjuster. In sunscreens it generally appears at low levels, often for pH control or mild surface conditioning rather than strong exfoliation.
Safety & warnings
Glycolic acid can be irritating, especially at higher concentrations and lower pH, and may cause stinging, redness, or dryness in sensitive skin. Because it promotes exfoliation, it can leave skin more sensitive to sun, so daily sun protection is advised; it is not a recognized fragrance allergen and is not an oil, so comedogenicity is not a concern.
Origin & sourcing
Glycolic acid can be derived from natural sources such as sugarcane but is most commonly produced synthetically for cosmetic use.
History
Alpha hydroxy acids, including glycolic acid, became widely used in cosmetics from the late twentieth century onward as exfoliating and skin-smoothing ingredients.
Questions everyone asks
Why is glycolic acid in a sunscreen?
At low levels it is often used to adjust the formula's pH or provide mild surface conditioning, rather than as a strong exfoliating treatment.
Can glycolic acid make skin sensitive to sun?
Yes, exfoliating acids can increase sun sensitivity, which is one reason consistent daily sun protection is recommended when using them.