L-ascorbic acid is the bioactive form but highly unstable in water. Sodium ascorbyl phosphate (SAP) is water-stable and skin-friendly but requires enzymatic conversion. Tetrahexyldecyl (THD) ascorbate is oil-soluble and very stable, making it ideal for anhydrous or emulsion formulas, though it is more expensive. Ascorbyl glucoside is extremely shelf-stable and hydrophilic but slower-acting. AJ Cosmo Labs can connect you with cosmetic chemists who have clinical experience with each derivative.
Read the full guide on Vitamin C formulation challenges →