Vitamin C + Collagen Serum Formulation

You've proposed a modified formula for a Vitamin C + Collagen serum, based on the Vitamin C serum formula (likely the Vitamin C E Ferulic type). While the idea of combining these beneficial ingredients is good, modifying established formulas, especially those containing sensitive ingredients like L-Ascorbic Acid, can significantly impact stability.

As previously advised by the staff, the original Vitamin C E Ferulic formula is carefully balanced for stability. Your proposed formula introduces several changes and additional ingredients, including:

• Collagen
• Triethanolamine (for pH adjustment)
• WaterLock
• Ethoxydiglycol
• Propylene Glycol
• Glycerin
• Laureth-23
• Different ratios of Hyaluronic Acid (Standard and Nano)

While your formula includes Ferulic Acid and Vitamin E, which are known to help stabilize L-Ascorbic Acid, the interaction of these with the new ingredients, particularly Collagen and the pH adjustment needed for L-Ascorbic Acid (ideally pH 2.0-4.0, with FDA requiring at least 3.5 for skin application) and the optimal pH range for Collagen (3.5-7.0), can be complex. L-Ascorbic Acid is highly sensitive to pH and prone to oxidation in water-based formulas.

Therefore, the stability and efficacy of your proposed formula cannot be guaranteed without thorough testing. It is strongly recommended that you perform comprehensive stability testing on your modified formula. This should include monitoring changes in color, clarity, viscosity, and pH over time and under various temperature conditions (e.g., room temperature, elevated temperature, freeze-thaw cycles) to ensure the product remains stable and effective before producing it for personal use or sale.