Sunscreen SPF Issue

It appears the primary reason for the low SPF (4.5) in your sunscreen formula, despite using 5% Zinc Oxide EasyDisperse and 5% Titanium Dioxide EasyDisperse, is likely due to the type of Titanium Dioxide used.

Based on the product information:

• Titanium Dioxide 200nm EasyDisperse™ is specifically recommended for makeup products only, not for sunscreen applications where UV protection is the primary goal. You need to use a type of Titanium Dioxide that is designed and tested for UV protection in sunscreen formulations.
• Zinc Oxide 200nm EasyDisperse™ is suitable for sunscreen, but achieving high SPF requires excellent dispersion. Ensure you are following the recommended mixing method, such as pre-dispersing in a silicone like Cyclomethicone (1:1 ratio), and consider using stabilizers like Xanthan Gum (0.2-0.3%) and Propylene Glycol (3-4%) to help ensure the particles are evenly distributed and stable in the formula. Poor dispersion significantly reduces SPF effectiveness.
• PMMA Booster is an SPF enhancer. It works by boosting the SPF provided by the primary UV filters (Zinc Oxide and Titanium Dioxide). While it can double the SPF at 5% usage, it cannot compensate for a very low base SPF caused by using an inappropriate UV filter or poor dispersion.

How to Increase SPF to 30-50

To increase your formula's SPF to the desired range (30-50), follow these steps:

1. Replace Titanium Dioxide: Substitute the Titanium Dioxide 200nm EasyDisperse™ with a grade of Titanium Dioxide specifically intended for sunscreen and UV protection.
2. Ensure Proper Dispersion: Make sure both your Zinc Oxide 200nm EasyDisperse™ and the new sunscreen-grade Titanium Dioxide are perfectly dispersed in your formulation. Follow product-specific mixing instructions carefully.
3. Adjust Concentrations: You will likely need to use a higher total concentration of the appropriate Zinc Oxide and Titanium Dioxide grades than 10% (5% + 5%) to reach SPF 30-50. The exact percentage will depend on the specific grades used and your overall formula.
4. Continue Using PMMA Booster: Keep the PMMA Booster at 5% as it will help enhance the SPF provided by the correctly selected and dispersed UV filters.

By addressing the type of Titanium Dioxide and ensuring optimal dispersion of both physical filters, you should be able to significantly increase the SPF of your sunscreen formulation.