Vitamin C Serum/Cream Formulation for Combination Skin: Stability and Texture

Based on the conversation with the staff, here is a summary of the answers to your questions regarding the Vitamin C repair serum formulation:

Regarding adding Vitamin B5 (Panthenol Pro Vitamin B5):

• You can add Vitamin B5 to the formula at a concentration of 1-5%, depending on how dry your skin is.
• It should be added to the water phase of the formulation.
• Your proposed mixing step of adding Vitamin B5 after water, Repair Activator, and Phenoxyethanol, then mixing, is correct.

Regarding substituting Perfect-C™ (Ascorbyl Tetraisopalmitate):

• You can substitute ingredients in the formula based on your budget and desired results.
• Perfect-C is oil-based, while Azelaic Acid (Liquid Azelaic™) is water-based. If you substitute Perfect-C with Azelaic Acid, you might also need to change the Silky Serum Base to a water-based type.
• Vitamin C (L-ascorbic acid) Ultra-Fine powder is not suitable for your proposed formula because this type of Vitamin C is unstable when dissolved in water.

Based on your skin type (oily T-zone, dry cheeks) and the instability of L-ascorbic acid in water, the staff recommended a revised cream formulation that balances the skin and uses a stable form of Vitamin C. Vitamin B5 was not included in this specific recommendation as other ingredients were suggested for balancing combination skin.

Here is the staff's recommended revised formula and mixing steps for a cream texture:

Recommended Formula:

1. Perfect-C TransDerm (Nourishing/Whitening): 10%
2. Vitamin B3 (Niacinamide) (Skin barrier repair): 5%
3. Repair Activator™ (Bifida Ferment Lysate): 10%
4. Zinc PCA (Oil control, balancing): 1%
5. Rice Vitamin (Inositol Vitamin B8) (Oil control, balancing): 3%
6. Pro Polymer (Acrylate Crosspolymer) (Thickener/Cream builder): 1.5%
7. Water: Remaining percentage
8. Phenoxyethanol (Preservative): 0.8%

Mixing Steps:

1. Combine ingredients 2, 3, 4, 5, 7, and 8 (Vitamin B3, Repair Activator, Zinc PCA, Rice Vitamin, Water, Phenoxyethanol) and mix until everything is dissolved and the mixture is clear.
2. Add ingredient 6 (Pro Polymer) and mix until a smooth gel is formed.
3. Add ingredient 1 (Perfect-C TransDerm) and mix until a cream texture is achieved.

The staff also noted that using 48% of Silky Serum Base as in your proposed formula would result in a very liquid texture; they suggested using around 10-15% for a good serum consistency if you were to use that base.

Therefore, your proposed formula using L-ascorbic acid powder is not recommended due to the ingredient's instability in water. The revised formula provided by the staff is suggested as a more suitable option for your skin type and desired outcome.