Calculating SPF/PA for Micronized Physical UV Filters in Powder

Determining the exact SPF and PA values for sunscreen ingredients like micronized Titanium Dioxide and Zinc Oxide is a complex process that typically involves testing the final product formulation rather than using a simple calculation based solely on the ingredient type or concentration.

While the concentration of the active ingredient is important, the final SPF and PA values are significantly influenced by factors such as:

• Particle size distribution and quality of dispersion in the base
• Interactions with other ingredients in the formulation
• The nature of the final product (e.g., cream, powder, lotion)
• The film formed on the skin after application

Standardized in vivo (on human skin) or in vitro (laboratory) testing methods are used to determine the actual SPF and PA values of a finished sunscreen product.

As noted in the previous discussion you shared, while the staff mentioned that values might be similar to nano versions when used in powder, this does not provide a specific calculation formula.

Therefore, a simple calculation method for micronized versions based purely on ingredient type and concentration is not available. The performance needs to be evaluated in the final formulation.