Validation of an in vitro sun protection factor (SPF) method in blinded ring-testing

Area of Science:

• Dermatology and Cosmetic Science
• Analytical Chemistry
• Regulatory Science

Background:

• The current In Vivo Sun Protection Factor (SPF) test method (ISO 24444:2010) is resource-intensive.
• Development of reliable in vitro SPF testing methods is crucial for efficient sunscreen product evaluation.
• Standardized acceptance criteria are needed to validate new in vitro SPF methodologies.

Purpose of the Study:

• To evaluate a novel in vitro SPF test method.
• To assess its performance against new International Standards Organization (ISO) acceptance criteria.
• To determine its suitability as an industry standard through blinded ring-testing.

Main Methods:

• Twenty-four commercial sunscreen products (SPF 6-50+) were tested using both the ISO 24444:2010 in vivo method and a new in vitro method.
• Testing was conducted by independent institutes and laboratories under blinded conditions.
• Results were analyzed for correlation and compared against ISO TC217/WG7 acceptance criteria.

Main Results:

• A strong correlation was observed between in vitro and in vivo SPF values (r² = 0.88, P < 0.0001).
• The new in vitro method demonstrated a strong correlation with in vivo SPF values, with a slope of 1.01 and a non-significant intercept.
• Over 95% of the data fell within the defined acceptance criteria 'funnel', indicating low method bias.

Conclusions:

• The new in vitro SPF test method successfully meets and exceeds the established ISO WG7 acceptance criteria.
• The method's strong performance in blinded ring-testing positions it as a promising candidate for industry-wide adoption.
• This in vitro method offers a reliable and potentially more efficient alternative to current in vivo SPF testing.