“My vitamin C serum has changed color. Is it still okay to use?”
The L-ascorbic acid (L-AA) form of vitamin C is one of the most extensively researched active ingredients in skin care, with research demonstrating its ability to deliver significant improvements to photoaged skin. L-AA fades hyperpigmentation, refines skin texture, stimulates increased collagen production for firmer and less wrinkled skin, and acts as a potent antioxidant, scavenging free radicals before they can damage cells and DNA.
Unfortunately, L-AA is also a difficult ingredient to work with. It’s notoriously unstable and prone to rapid degradation with exposure to air and light. That degradation appears as the darkening of an L-AA product over time from a clear or pale champagne color to a dark reddish brown, indicating advanced oxidation of the key ingredient.
While the L-ascorbic acid (L-AA) form of vitamin C is one of the most extensively researched active ingredients in skin care, it’s also a difficult ingredient to work with.
Oxidative stress in the body (including the skin) is caused by free radicals, which are highly reactive atoms with unpaired electrons. Generated by environmental factors like UV exposure, pollution, and ingested substances as well as by many natural processes of the body, free radicals take electrons where they can, including from cells and DNA, causing damage wherever they go.
Antioxidants like L-AA neutralize these free radicals by donating electrons to them before they take electrons from your cells, proteins, and DNA—they prevent oxidation within your body by sacrificing themselves instead.
The process isn’t always visible to the naked eye, but it is with L-AA. The more oxidized an L-AA product is, the darker and more brown it will appear. Oxidation converts L-AA into dehydroascorbic acid, and while some of that does convert back to L-AA in the skin, it will be less than the initial concentration of L-AA included in the vitamin C product.
While there is some fearmongering about whether using oxidized L-AA may increase damage to skin, the research doesn’t support this. The chief drawback of using an oxidized L-AA product will be reduced effectiveness due to the reduction in L-AA available to skin as well as the increased pH of the product as L-AA oxidizes to dehydroascorbic acid.
How to Delay Oxidation & When to Stop Using an Oxidized L-AA product
Because L-AA is so extensively researched, formulators have a good handle on how to stabilize this finicky ingredient. Formulating it at a low pH and using tocopherol (vitamin E) and ferulic acid alongside the L-AA are some of the most reliable ways to extend its shelf life. Using dark or opaque packaging further helps to protect it from degradation, since L-AA is so sensitive to light. Looking for a vitamin C serum that also contains vitamin E and ferulic acid and is packaged in a dark or opaque bottle are therefore the best ways to get the most use out of your L-AA.
Once your L-AA serum is in hand, you can further extend the shelf life by keeping it capped tightly and stored in a dark, cool place as well. I like keeping mine in the refrigerator. I find that as long as a vitamin C L-AA product arrives still fairly pale to champagne-colored, I can get through an entire bottle without serious oxidation.
Oxidation will still occur, so don’t be stingy with your use of an L-AA product—there’s no point in attempting to ration it out so that a bottle will last longer. Use your vitamin C serum daily, and don’t neglect your neck and upper chest. And pay attention to the color of the product. While there doesn’t seem to be a consensus on just how oxidized is too oxidized to expect continued benefits, I generally discontinue use if the product gets darker than a medium yellow.
The Bottom Line
The bottom line is this: L-AA is an excellent skin care ingredient when formulated appropriately and packaged correctly. While oxidation is inevitable, you can get plenty of use out of a vitamin C L-ascorbic acid product before it becomes too oxidized to use. Just store it carefully and use it consistently, and enjoy the results!