Why Does Topical Vitamin C Need a pH Below 3.5?
The pH 3.5 threshold is not an industry convention: it comes from a percutaneous absorption study that also fixed the concentration ceiling and the application schedule.
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Is Lipid-Soluble Vitamin C More Stable Than L-Ascorbic Acid?
Lipid solubility solves how vitamin C crosses the skin barrier. It does not solve how long the molecule survives once oxidised. What the published evidence actually...