What's the difference between L-ascorbic acid and vitamin C derivatives?

L-ascorbic acid is the pure, most-studied form but is unstable and can sting or oxidize quickly. Derivatives such as ascorbyl glucoside, sodium ascorbyl phosphate, and THD ascorbate are more stable and gentler, though they generally require conversion in the skin and may act more slowly. Sensitive-skin users often prefer derivatives; those chasing maximum potency lean toward L-ascorbic acid.