Sunscreen Formulation Issues: Solubility, Texture, and Manufacturing Steps

Subject: Feedback and Analysis of Sunscreen Formula

Thank you for sharing your sunscreen formula and questions. This formula aims to combine physical and chemical filters for broad-spectrum protection and a better texture, which is a good approach.

Let's address your questions based on the formula provided and the staff's valuable feedback:

1. Ingredient Compatibility and Percentages:

   • The combination of TiO2 (physical filter) with Avobenzone and Octocrylene (chemical filters) is suitable for achieving broad-spectrum UV protection (UVA/UVB) and helping reduce the white cast often associated with high levels of physical filters alone.
   • Important Point (as highlighted by staff): The formula lacks sufficient solvent for Avobenzone (3%). Avobenzone requires specific oil-soluble solvents to be fully dissolved and stable. Without adequate solvation, it may not provide the intended protection and could potentially crystallize over time. You need to incorporate a suitable solvent for Avobenzone into the oil phase. Please check the product page for Avobenzone for recommended solvents.
   • SiliSolve Plus (1%): As the staff mentioned, SiliSolve Plus is likely unnecessary in this formula. TiO2 15nm Liquid is often pre-dispersed and stabilized, and Pro Polymer can help stabilize the overall emulsion. Removing SiliSolve Plus can simplify the formula.
   • Pro Polymer (1.5%): The staff correctly pointed out that 1.5% Pro Polymer is quite high for a sunscreen, which should ideally be easy to spread. While it will certainly thicken the formula, it might result in a texture that is too thick or even slightly gummy, making application difficult and potentially leading to uneven coverage (and thus uneven protection). The staff's recommendation to use around 0.5% is a good starting point for achieving a suitable viscosity.
   • Other ingredients like 2Na-EDTA (chelating agent), Cyclomethicone and LipidSoft Lite (emollients/texture enhancers), Phenoxyethanol SA (preservative), and Madecassoside (soothing agent) are generally compatible in this type of formulation, provided the emulsion system is stable and the Avobenzone is properly dissolved.

2. Texture with 60% Water:

   • Your concern about 60% water making the texture too thin is understandable, but the final viscosity is heavily influenced by the thickeners and emulsifiers used.
   • With 1.5% Pro Polymer, the formula would likely not be too thin; in fact, as mentioned above, it would likely be too thick.
   • By reducing Pro Polymer to a more appropriate level (e.g., 0.5% as suggested by staff), the texture will be less viscous than with 1.5%, but the goal is to achieve a balance that is spreadable and comfortable, not overly thick. The staff's suggested process (emulsifying first, then thickening) allows you to control the final viscosity by adjusting the Pro Polymer amount added.

3. Manufacturing Steps:

   • Your proposed steps are a good attempt, but the staff's suggested method is generally more suitable for creating a stable emulsion with dispersed pigments and dissolved chemical filters.
   • Staff's Suggested Process (Recommended):
     • Combine all oil-soluble ingredients, including Cyclomethicone, LipidSoft Lite, Avobenzone, Octocrylene, and the TiO2 15nm Liquid. Heat this oil phase to 70-80°C and mix well to ensure Avobenzone is dissolved and TiO2 is well-dispersed.
     • Prepare the water phase by combining Water and 2Na-EDTA. Heat this water phase to 70-80°C.
     • Slowly add the water phase to the oil phase while mixing vigorously (high shear mixing is best if available) to form the emulsion. Continue mixing until the emulsion cools down.
     • Once the emulsion has cooled significantly (e.g., below 40°C), add the Pro Polymer powder while mixing. Continue mixing until the gel forms and the desired viscosity is achieved. Note: You can adjust the amount of Pro Polymer here to control thickness.
     • Finally, add heat-sensitive ingredients like Madecassoside -80 powder and Phenoxyethanol SA, and mix until fully incorporated.
   • Why the Staff's Method is Better: This method ensures that the oil-soluble UV filters and the dispersed TiO2 are properly incorporated into the oil phase before emulsification, leading to a more stable and effective product. Adding the water phase to the oil phase is a common technique for creating W/O (Water-in-Oil) emulsions, which can offer good water resistance, although O/W (Oil-in-Water) is also possible depending on the emulsifier system (which isn't explicitly listed here, but SiliSolve Plus was an emulsifier, now removed). The staff's method seems geared towards properly handling the UV filters and pigment.
   • Regarding Silicone Gel (Vinyl Dimethicone Crosspolymer): This ingredient was mentioned in your steps and viscosity question but not your initial ingredient list. If you intend to include it, it is typically added to the oil phase or silicone phase. It primarily contributes to the feel and can thicken the silicone/oil phase, but Pro Polymer is the main thickener for the water phase and overall viscosity in this formula structure.
   • Adjusting Viscosity: As discussed, adjusting the percentage of Pro Polymer is the most direct way to control the overall viscosity of the final cream/gel. Start with the staff's suggestion of around 0.5% and adjust up or down in small increments in future trials until you achieve the desired spreadability and texture.

4. SPF/PA Calculation:

   • Your calculated SPF of 35 and PA+++ is a good theoretical estimate based on the percentages of UV filters.
   • However, as mentioned regarding Avobenzone solubility, the actual protection achieved in the final product can be lower than the theoretical calculation if the UV filters are not properly dissolved, dispersed, and stable within the formulation. Ensuring Avobenzone is fully dissolved is crucial for achieving the calculated SPF/PA.

Summary of Recommendations:

1. Address Avobenzone Solubility: Incorporate a suitable solvent for Avobenzone into the oil phase.
2. Remove SiliSolve Plus: It is not needed in this formula.
3. Reduce Pro Polymer: Start with a lower percentage, around 0.5%, and adjust as needed for desired viscosity.
4. Follow Staff's Manufacturing Process: Combine oil phase ingredients (including UV filters and TiO2 liquid), heat, combine water phase ingredients, heat, add water phase to oil phase with mixing to emulsify, cool, add Pro Polymer to thicken, add heat-sensitive ingredients.
5. Adjust Viscosity: Use Pro Polymer percentage to fine-tune the final texture.

By making these adjustments, you should be able to create a more stable and effective sunscreen with a better texture that meets your objectives.