Combining Titanium Dioxide and Zinc Oxide for Sunscreen

Combining Titanium Dioxide and Zinc Oxide in a sunscreen formulation is an excellent approach to achieve broad-spectrum protection against both UVA and UVB rays. Titanium Dioxide primarily offers strong protection against UVB and some UVA II rays, while Zinc Oxide provides broader coverage across the UVA and UVB spectrum, including UVA I.

Regarding your question about using 12.5% Titanium Dioxide and 12.5% Zinc Oxide to achieve SPF 50++, simply splitting the percentage of the original Titanium Dioxide concentration does not guarantee a specific SPF level. The final SPF and PA values of a sunscreen formulation depend on several factors, including:

• The specific types and particle sizes of the Titanium Dioxide and Zinc Oxide used.
• The ratio of Titanium Dioxide to Zinc Oxide.
• The overall formulation base and how well the UV filters are dispersed.
• The total concentration of active UV filter ingredients.

The staff's previous reply indicated that your original formula using 25% nano Titanium Dioxide is expected to provide an SPF of approximately 45 and PA+++.

To achieve a higher SPF, such as SPF 50++, you would typically need to use a higher total concentration of UV filters or optimize the ratio of Titanium Dioxide and Zinc Oxide in your specific formulation. For example, some forms of Zinc Oxide dispersion can be used up to 50% in a formula (while respecting the FDA limit of 25% active Zinc Oxide), and certain Titanium Dioxide dispersions can also be used at high rates. However, the optimal percentages and ratio must be determined through formulation testing to confirm the desired SPF and PA levels.

You can refer to the sample formula for Physical Sunscreen provided by the staff as a starting point, which is formulated to achieve SPF ~45 and PA+++. Adjusting the concentrations and ratios of the UV filters from there, followed by testing, would be necessary to aim for SPF 50++.