New approach for a reliable in vitro sun protection factor method - Part II: Practical aspects and implementations

Area of Science:

• Dermatology
• Cosmetic Science
• Photobiology

Background:

• Previous research established a reproducible in vitro sun protection factor (SPF) method correlated with in vivo results.
• An internationally relevant SPF method requires adaptability across diverse commercial sunscreen formulations.

Purpose of the Study:

• To validate a novel in vitro SPF method for practical application on a wide range of sunscreen products.
• To demonstrate the method's ability to yield results comparable to in vivo SPF measurements for labeling purposes.

Main Methods:

• Spectroradiometric measurement of residual ultraviolet (UV) transmission through sunscreen samples applied robotically to a substrate.
• Utilized a multisubstrate solution with a single UV pre-irradiation dose for enhanced reliability.
• Evaluated the method across five distinct sunscreen categories: emulsions, oils, alcohol-based, sticks, and powders.

Main Results:

• The in vitro SPF method demonstrated good reproducibility and accuracy, with a mean coefficient of variation (CV%) of approximately 7%.
• High coefficients of correlation (0.8-1.0) were achieved between the in vitro method and clinical SPF measurements across all tested product types.
• The method proved effective for diverse formulations, including emulsions, oils, alcohol-based products, sticks, and powders.

Conclusions:

• The developed in vitro SPF method is suitable for SPF labeling of all sunscreen product types.
• The method offers advantages of being non-invasive, cost-effective, practical, and reliable when conducted under stringent conditions.
• Validation across 113 sunscreen products in Parts I and II supports its broad applicability for regulatory and commercial use.