Rapid Oxidation of Homemade Vitamin C Serum and Usability
Question
I made a homemade Vitamin C serum based on the Skinceuticals C E Ferulic formula with a pH of 3.5. I stored it in a dark bottle at room temperature. Within 11 days, the serum turned a dark color, much darker than Oishi green tea, indicating rapid oxidation. I have the following questions:
- Why did the serum oxidize so quickly?
- Is the oxidized serum still usable?
- Has its effectiveness significantly decreased?
- How long should a Vitamin C serum normally last when stored in the refrigerator?
- Could there have been a mistake in my preparation process?
Answer
Hello,
Thank you for the detailed information about your homemade Vitamin C serum based on the Skinceuticals C E Ferulic formula.
The rapid and significant color change you observed, turning darker than Oishi green tea within 11 days, is a clear indication of significant Vitamin C oxidation.
As previously mentioned by the staff, the main reasons for this rapid oxidation are likely:
- Lack of refrigeration: Vitamin C serums, especially homemade ones, are highly sensitive to temperature. Storing them at room temperature significantly accelerates degradation.
- Light exposure: Even indirect light can contribute to oxidation. While you used a dark bottle, if it wasn't completely opaque or if it was frequently exposed to ambient light, it could still be a factor, although lack of refrigeration is usually the primary culprit for such rapid change.
Regarding your questions:
- Why did it oxidize so quickly? As explained above, lack of refrigeration and light exposure are the main reasons. Vitamin C (L-Ascorbic Acid) is inherently unstable, and these conditions speed up its degradation into inactive forms.
- Is it still usable? When a Vitamin C serum turns a dark yellow, orange, or brown color, it means the L-Ascorbic Acid has largely oxidized. While it might not be harmful, its effectiveness as an antioxidant and collagen booster is significantly reduced or completely lost. It is generally recommended not to use a serum that has oxidized to this extent.
- Has the effectiveness significantly decreased? Yes, the dark color indicates that most of the active Vitamin C has degraded, meaning its effectiveness is greatly diminished.
- How long does it normally take to oxidize when stored in the refrigerator? With proper storage (refrigerated, in an airtight, opaque container), a well-formulated L-Ascorbic Acid serum should last much longer, typically around 3-6 months. During this time, a slight yellowing might occur, especially towards the end of its shelf life, often due to the oxidation of Vitamin E in the formula, but it should not turn dark brown.
- Did you make a mistake? Based on your description, your pH of 3.5 is appropriate for L-Ascorbic Acid stability and skin penetration. If you are confident you followed the formula and steps correctly, the issue is most likely related to storage conditions rather than the preparation itself.
In summary: Your serum oxidized rapidly due to storage conditions (lack of refrigeration being a major factor). The dark color means it has lost most of its potency and should likely not be used. For future batches, always store the serum in the refrigerator in an airtight, opaque bottle to maximize its shelf life and effectiveness.