Vitamin C Serum Discoloration and Stability Without Refrigeration

Subject: Vitamin C Serum Discoloration

Hello,

Thank you for your question regarding the yellowing of your Vitamin C E Ferulic serum.

It is common for serums containing L-Ascorbic Acid (Vitamin C) to change color over time, turning yellow or brown. This is due to oxidation of the Vitamin C, which reduces its effectiveness. Several factors accelerate this process, including exposure to light, air, heat, and importantly, the pH level of the formulation.

You mentioned that storing the serum in the refrigerator prevents the color change, which confirms that temperature is a significant factor.

Regarding your question about adjusting the ingredients to prevent color change without refrigeration, the most critical factor for L-Ascorbic Acid stability is the pH of the serum. L-Ascorbic Acid is most stable and effective in formulations with a low pH, typically between 2.5 and 3.5.

Your formula includes Triethanolamine (2.5%), which is a basic ingredient used to adjust pH. Its presence likely raises the pH of your serum above the optimal range for L-Ascorbic Acid stability, accelerating oxidation and color change at room temperature.

To improve the stability of your serum without refrigeration, the primary adjustment should be to lower the pH by reducing or potentially removing the Triethanolamine from your formula. You will need to measure the pH of the final serum after adjusting the Triethanolamine concentration to ensure it falls within the 2.5-3.5 range. Please note that adjusting the pH might affect the texture or feel of the serum.

Other factors to consider for improving stability include:

• Water Purity: Ensure you are using highly purified water with very low TDS (Total Dissolved Solids), as metal ions in impure water can catalyze oxidation.
• Packaging: Continue using dark glass bottles to protect from light. Minimize the amount of air in the bottle.
• Manufacturing Process: Minimize heat exposure during mixing. While some heat might be necessary to dissolve ingredients like Laureth-23, try to keep the overall temperature as low as possible and cool the mixture quickly before adding heat-sensitive ingredients like Vitamin E and L-Ascorbic Acid.

Even with these adjustments, L-Ascorbic Acid serums are inherently unstable compared to other forms of Vitamin C. Refrigeration remains the most effective method to significantly extend the shelf life and prevent discoloration.

We recommend experimenting with reducing Triethanolamine to achieve a lower pH and observing the stability.