Serum Color Change and Formula Improvement

1. Cause of Color Change

The rapid yellowing of your serum is most likely due to the oxidation of Retinal (Retinaldehyde). Retinal is a highly effective but unstable form of Vitamin A that is very sensitive to light and air. Even if stored in a dark corner, using a clear plastic bottle exposes the serum to ambient light during use and storage, accelerating its degradation and causing the color change. While Vitamin E is an antioxidant, the concentration in your formula might not be sufficient to fully stabilize the Retinal.

2. Changing the Emulsifier

You asked about changing from Silky Serum Base Plus to Satin Cream Maker.

• Silky Serum Base Plus is a serum base suitable for light textures and can handle the oil/silicone load in your current formula (8% Shea Butter Light Oil + 4% Cyclomethicone + 10% Silky Serum Base Plus = 22% total oil/silicone phase).
• Satin Cream Maker is a cream maker that can also handle your oil/silicone load (up to 25% oil and 20% silicones) and would likely result in a thicker, creamier texture, which might be suitable for dry skin.
  Switching to Satin Cream Maker would change the texture of your product from a serum to a cream, but it will not directly solve the color stability issue caused by Retinal oxidation. The choice depends on your desired final product texture.

3. Necessity of Flora Solve

Flora Solve Clear is a solubilizer used to mix fragrance or essential oils into water-based formulas. Your current formula does not contain added fragrance or essential oils. Shea Butter Light Oil is an oil that is compatible with the Silky Serum Base Plus (or Satin Cream Maker if you switch). Therefore, Flora Solve Clear is not necessary for this formula.

4. Odor Masking Agents

If the serum has a strong odor, it might be coming from the raw materials, possibly the Retinal itself or other ingredients. Since you prefer not to use fragrance, you can consider using an odor masking agent.

• Odor-Kill is water-soluble and effective at absorbing general ingredient odors. However, be aware that it can also absorb fragrance if you decide to add it later.
• Citromask is oil-soluble and works well for fatty acid odors.
  Choose the one that seems most suitable based on the type of odor you are experiencing.

5. Recommended Formula Adjustments for Dry Skin and Stability

To improve the formula for dry skin and address the color stability issue:

• Prevent Color Change:
  • Packaging: The most crucial step is to use an opaque bottle that protects the serum from light exposure. Clear bottles are not suitable for formulations containing light-sensitive ingredients like Retinal.
  • Antioxidants/Stabilizers: Add a dedicated antioxidant blend to protect the Retinal from oxidation. Consider adding Protec OX (oil-soluble) or ActiveProtec OX (water-soluble). Since your formula is an emulsion containing both water and oil phases, using both might provide better protection.
  • For additional protection against light (if an opaque bottle is not possible, though highly recommended), you could also add a UV absorber like Protec UV (oil-soluble) or Protec SQ (oil-soluble, also a singlet state quencher).
  • Bakuchiol is also known to help stabilize Retinal.
• Enhance for Dry Skin:
  • Increase the percentage of Shea Butter Light Oil if your chosen emulsifier can handle a higher oil load.
  • Consider adding other emollients or occlusive agents suitable for dry skin.
  • If you switch to Satin Cream Maker, the resulting cream texture will inherently feel richer and more moisturizing, which is beneficial for dry skin.

Example of potential adjustments (percentages would need testing):

• Reduce water slightly to accommodate additional oil/emollients.
• Increase Shea Butter Light Oil or add another oil/butter.
• Add Protec OX (e.g., 0.05%) and/or ActiveProtec OX (e.g., 0.5-1%).
• (Optional, if not using opaque bottle) Add Protec UV (e.g., 0.1%) and/or Protec SQ (e.g., 3-5%).
• (Optional) Add Bakuchiol (e.g., 0.5-1%) for synergistic effects and stabilization.
• If switching to Satin Cream Maker, adjust its percentage based on the total oil phase to achieve the desired cream viscosity.

Always perform stability testing on your final formulation to ensure the color remains stable over time and that the product is safe and effective.