Formulating Physical Sunscreen with Zinc Oxide and Titanium Dioxide: Addressing White Cast and SPF/PA

The user inquired about formulating a physical sunscreen with Zinc Oxide (ZiO) and Titanium Dioxide (TiO2), experiencing a white cast ("wook") and asking about the roles of each ingredient.

Key points from the discussion:

• UV Protection: Zinc Oxide provides broader protection, covering UVA rays more effectively than Titanium Dioxide. Titanium Dioxide is generally better at blocking UVB rays. SPF measures UVB protection, while PA measures UVA protection. Both UVA (causes aging) and UVB (causes sunburn) protection are important.
• Formulation: Using both ZiO and TiO2 together is common and recommended to achieve broad-spectrum UVA/UVB protection.
• Whiteness: Titanium Dioxide tends to contribute more to the white cast than Zinc Oxide.
• Particle Size: The Zinc Oxide and Titanium Dioxide products discussed are micronized or have particle sizes (around 200nm and 100-200nm) larger than the <100nm size debated for potential absorption issues, and are considered safe.
• Recommendation: To minimize whiteness while achieving desired SPF/PA, it is recommended to add Titanium Dioxide up to an acceptable level of whiteness, and then add Zinc Oxide for the remaining required protection. Chemical sunscreens can also be added if needed.

The user found the information helpful and plans to purchase the ingredients.