Formula Evaluation for Clear, Hydrating, and Brightening Essence

Your proposed formula includes excellent ingredients targeting hydration and brightening, and most are water-soluble, aligning with your goal for a clear, non-sticky essence. The combination of Ethyl Ascorbic Acid and Licorice Extract (Glabridin) is good for brightening, while Double Hyaluron Liquid, Rhamnose, and Probio-Protect contribute well to hydration and skin conditioning.

However, there are a few points to consider and potentially adjust to ensure the formula meets your desired characteristics and stability:

• Madecassoside Solubility: You've included Madecassoside 80 (using Centella Asiatica Extract (Madecassoside 90%)) at 2%. According to the product description, Madecassoside 90% is only soluble in water up to 1.0% w/v. Using it at 2% will likely result in the powder not fully dissolving, making your essence cloudy or requiring a suspending agent to keep the particles dispersed. If you want a truly clear essence, you should reduce the concentration of Madecassoside 90% to 1% or less.

• Ethyl Ascorbic Acid Stability: The description for Ethyl Ascorbic Acid recommends including 0.2% Disodium EDTA in the formula when using water to help stabilize the Vitamin C derivative. Your current formula does not include EDTA. Adding 0.2% Disodium EDTA is highly recommended to maintain the stability and efficacy of the Ethyl Ascorbic Acid over time.

• pH Level: The ingredients have different optimal or required pH ranges for stability and efficacy. Ethyl Ascorbic Acid requires pH 3.5-6.0, Rhamnose is pH 5-9, Double Hyaluron Liquid is pH 3-9, and Madecassoside 90% is pH 4-6.5. You will need to check the pH of your final mixture and adjust it to a range that is compatible with all ingredients, ideally around pH 5.0-5.5, which falls within the acceptable range for most of these ingredients. However, note that the optimal pH for Ethyl Ascorbic Acid efficacy might be slightly lower, so balancing efficacy and ingredient compatibility is key.

• Mixing Procedure: Some ingredients, such as Licorice Extract (Glabridin 4.5%), Madecassoside 90%, and Probio-Protect, should not be exposed to heat. Ensure these are added during the cool-down phase of your formulation process.

• Preservation: You are using Probio-Protect at 2%, which is within the recommended usage rate for preservation. However, it is always recommended to perform challenge testing on your final formula to ensure the preservative system is effective against microbial growth in your specific product.

• Texture with Hyaluron: 15% Double Hyaluron Liquid is a relatively high concentration, recommended for very dry skin. While it's a liquid form, this concentration might result in a slightly thicker texture than a very watery essence, though it should still be clear and not overly sticky if formulated correctly.

Summary of Recommendations:

1. Reduce Madecassoside 90% to 1% or less for a clear solution, or accept a potentially cloudy/dispersed product at 2% (which may require a suspending agent).
2. Add 0.2% Disodium EDTA for Ethyl Ascorbic Acid stability.
3. Check and adjust the final pH to approximately 5.0-5.5.
4. Add heat-sensitive ingredients in the cool-down phase.
5. Perform challenge testing to confirm preservation efficacy.

By considering these points, you can refine your formula to better achieve a clear, stable, and effective hydrating and brightening essence.