Vitamin C derivatives are modified forms of ascorbic acid built to solve its two practical problems: it oxidizes quickly, and at the low pH it needs to work it can sting. The common ones you will see on a Korean or Japanese label include ascorbyl glucoside, 3-O-ethyl ascorbic acid, sodium ascorbyl phosphate, magnesium ascorbyl phosphate and ascorbyl tetraisopalmitate.Each behaves differently. Stability studies consistently show derivatives holding up far better in a finished product than pure ascorbic acid, and the phosphate forms are among the more stable. The trade-off is conversion: a derivative has to be taken up by skin and converted back to ascorbic acid to act as an antioxidant, and how efficiently that happens varies by molecule and is not always well documented. Ethyl ascorbic acid carries an unusually high proportion of usable vitamin C by weight, which is why it appears so often in newer formulas.Brands tend to present derivatives simply as vitamin C, sometimes implying equivalence with a 15 or 20 percent L-ascorbic acid serum. That equivalence is not established. What is fair to expect is gradual improvement in dullness and uneven tone with much less irritation and a product that does not turn brown in six weeks.Derivatives suit sensitive and dry skin, first-time vitamin C users, and anyone who has abandoned a pure ascorbic acid serum because of stinging or oxidation. They are less compelling if you tolerate L-ascorbic acid well and want the version with the deepest clinical file.They combine easily with niacinamide, glutathione, hyaluronic acid and peptides, and they work well in the morning under sunscreen. Give any vitamin C product eight to twelve weeks before judging it.Ours are paired with glutathione in the numbuzin No.5 Glutathione Vitamin Dark Spot Cream.

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