Serum Formulation Guidance

Based on your ingredients (Alpha Arbutin, Ethoxydiglycol, Vitamin B3, Distilled Water) and your goal of making a skin serum, here is some guidance:

Suggested Formula Adjustments

Your current formula uses Ethoxydiglycol at 20%, which is higher than the typical recommended usage rate for leave-on cosmetic products (usually not exceeding 2.6%). While Ethoxydiglycol is a good solvent and carrier, using it at such a high concentration might not be necessary and could potentially cause issues. You may consider reducing the amount of Ethoxydiglycol.

To improve the formula, it is highly recommended to add:

• Glycerin: This acts as a humectant, helping to draw moisture into the skin and improve the serum's texture and hydration properties. A typical usage rate is 2-10%.
• Preservative: A water-based formula like this requires a preservative to prevent bacterial and fungal growth. Options include Phenoxyethanol or Phenoxyethanol SA. Use according to the recommended rate (typically 0.5-1.0%).

Here is an example of an adjusted formula (adjust percentages to total 100%):

• Alpha Arbutin: 2%
• Vitamin B3 (Niacinamide): 10%
• Ethoxydiglycol: ~2.5% (adjust based on desired solubility and regulatory limits)
• Glycerin: ~5%
• Preservative (e.g., Phenoxyethanol): ~1%
• Distilled Water: Balance (adjust to make total 100%)

Mixing Order

For a water-based serum with these ingredients, a general mixing order is:

1. Combine the water phase ingredients: Distilled Water, Ethoxydiglycol, and Glycerin.
2. Add Vitamin B3 (Niacinamide) to the water phase and stir until fully dissolved. Gentle warming (below 60°C) can help, but avoid prolonged heat.
3. Ensure the mixture has cooled to below 30°C.
4. Add Alpha Arbutin and stir until fully dissolved.
5. Add the preservative and stir to combine.
6. Important: Check the pH of the final serum. Alpha Arbutin is most stable and effective in a pH range of 3.5-6.5, and Niacinamide is best between 4.0-7.0. The optimal overlapping range is 4.0-6.5. If the pH is outside this range, adjust it using a suitable pH adjuster (e.g., Lactic Acid or Citric Acid solution to lower pH, Sodium Hydroxide solution to raise pH).

Additional Considerations

• pH Adjustment: This is crucial for the stability and efficacy of Alpha Arbutin and Niacinamide. Always check and adjust the pH.
• Stability: Store the finished serum in a cool, dark place, ideally in an opaque bottle, to maintain ingredient stability.
• Patch Testing: As a beginner, always perform a patch test on a small area of skin before applying the serum to your face.

Adding Glycerin and a preservative will make your serum more complete and stable. Remember to check the recommended usage rates for all ingredients you use.