Oxidation is the primary cause. L-ascorbic acid degrades to dehydroascorbic acid and then to diketogulonic acid, which produces characteristic yellow-to-brown discoloration. Triggers include dissolved oxygen, trace metal ions, UV exposure, and high pH. Chelating agents, antioxidant boosters like ferulic acid, and airless or opaque packaging slow this significantly. A cosmetic chemist found through AJ Cosmo Labs can recommend the right stabilization strategy for your specific formula system.
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