— § 01
What L-ascorbic acid actually is.
L-ascorbic acid is vitamin C in its biologically active L-stereoisomer. It is the only form the human cell uses directly — every other "vitamin C" on a label is a derivative that must convert to LAA inside the skin, with conversion rates ranging from genuine to negligible. The molecule is simultaneously skincare's most useful antioxidant and its most temperamental one: pH-dependent for absorption, oxygen-sensitive in storage, and easily inactivated by water, heat, and time on a shelf.
When formulated correctly — the SkinCeuticals C E Ferulic patent of 15% LAA, 1% α-tocopherol, 0.5% ferulic acid at pH ≤ 3.5 is the reference — it provides the strongest published in-vivo evidence for any over-the-counter daytime antioxidant. When formulated badly, you have brown water in a clear bottle.