Serum Formulation Advice

Your proposed formula contains a mix of water-soluble ingredients (Vitamin C, Glutathione, Alpha Arbutin) and a silicone that does not dissolve in water (Cyclomethicone/Cyclopentasiloxane). Combining these two types of ingredients requires specific considerations.

Key Issues with the Current Formula

1. Lack of Emulsifier: As the staff correctly pointed out, you are missing an emulsifier. Water and silicone/oil phases will separate without an emulsifier to bind them together into a stable emulsion (like a cream or lotion). Given the high percentage of both water and silicone, you would need an emulsifier system capable of creating a stable emulsion, possibly a water-in-silicone or silicone-in-water emulsion depending on the chosen emulsifier.
2. Lack of Preservative: Any formula containing water must include a broad-spectrum preservative to prevent the growth of bacteria, mold, and yeast, which can spoil the product and be harmful to the skin.
3. Ingredient Stability and Compatibility:
   • Vitamin C (L-ascorbic acid): This form of Vitamin C is highly effective but also highly unstable, especially in water. It requires a low pH (ideally 3.5-4.0 for cosmetic use) to remain stable and effective. It is also prone to oxidation when exposed to light and air.
   • Glutathione: This ingredient is water-soluble and is most stable in a pH range of 3-6. It should be mixed without excessive heat.
   • Alpha Arbutin: This is also water-soluble and is stable in a pH range of 3.5-6.5. At a pH higher than 8, it can break down into hydroquinone. The product description recommends using ActiveProtec™ OX to help prevent discoloration.
   • Combining these actives means you need to find a pH that offers a reasonable balance for all three. A pH around 3.5-4.0, while optimal for L-Ascorbic Acid, is at the lower end for Alpha Arbutin and within the range for Glutathione. This pH range is generally acceptable for efficacy and stability of this combination, but requires careful formulation.

Recommended Adjustments

To make this formula viable and stable, you need to make the following additions and considerations:

1. Add an Emulsifier: Select an emulsifier or emulsifier blend suitable for creating an emulsion with both a water phase and a silicone phase. The choice will depend on the desired texture and the ratio of water to silicone.
2. Add a Preservative: Include a broad-spectrum preservative system effective at the final pH of your formula.
3. Adjust and Control pH: Carefully adjust the pH of the final formula to be within the range of 3.5-4.0 to ensure the best possible stability and efficacy for L-Ascorbic Acid, while remaining acceptable for Glutathione and Alpha Arbutin. You will need a pH meter to accurately measure and adjust the pH.
4. Consider Stabilizers/Antioxidants: To further protect the active ingredients from degradation, especially Vitamin C and Alpha Arbutin, consider adding antioxidants like ActiveProtec™ OX or Protec™ OX.
5. Manufacturing Process: The order and method of mixing are crucial, especially for temperature-sensitive and pH-sensitive ingredients like L-Ascorbic Acid and Glutathione. They should typically be added in the final cooling phase after the emulsion is formed and the pH is adjusted.

Summary

Your proposed formula contains good active ingredients for skin brightening. However, it is not a complete or stable formulation as it lacks essential components like an emulsifier and a preservative. Additionally, careful attention must be paid to the pH and stability of the active ingredients. You will need to add an appropriate emulsifier, a preservative, and adjust the pH to create a stable and effective serum.