Ingredient Compatibility and Stability at pH 3.5

Based on your revised formula and the staff's feedback, here are the key points regarding ingredient compatibility and stability at a target pH of 3.5:

• Wild Yam Extract: This ingredient's optimal pH range is 4-6.5. While it might degrade faster at pH 3.5, it should be acceptable for personal use within approximately 6 months.
• Ferulic Acid: Ferulic Acid, even when dissolved in Ethoxydiglycol, is not directly soluble in water. Adding this mixture to the water phase will cause precipitation or crystallization.
• Glutathione: Glutathione dissolves in water, but it can be slow. Gentle warming (50-60°C) can help. Your observation of precipitation when Glutathione was present was likely due to the Ferulic Acid's insolubility in water, not a direct incompatibility with Glutathione.
• Formula Stability: With approximately 50% water content, the formula might not be stable long-term and could separate. The staff recommends increasing the water phase to at least 60% for better stability.

Correct Mixing Method for Ferulic Acid:

To prevent precipitation, dissolve Ferulic Acid in Ethoxydiglycol separately. Prepare your serum base (water phase with water-soluble ingredients like Glutathione, and oil phase). Add the Ferulic Acid/Ethoxydiglycol mixture to the finished serum base at the very end and mix thoroughly.