The revised COLIPA in vitro UVA method.

Area of Science:

• Dermatology
• Cosmetic Science
• Photobiology

Background:

• Standardized in vitro testing is crucial for evaluating UVA protection factor (UVAPF).
• Previous methods using low-roughness plates showed good correlation but potential for improvement in accuracy and reproducibility.
• Optimizing in vitro UVA testing conditions is essential for reliable sun protection product assessment.

Purpose of the Study:

• To assess the influence of test conditions, specifically plate roughness, on UVA protection factor (UVAPF) values.
• To compare the amplitude, reproducibility, and correlation with in vivo results of two different in vitro UVA testing conditions.
• To determine the optimal plate type for the COLIPA in vitro UVA method to enhance accuracy and limit variability.

Main Methods:

• A multicentered study utilized the COLIPA in vitro UVA method with eight sunscreen products.
• Two types of plates were tested: high-roughness (5 μm) and low-roughness (2 μm), with different application rates.
• UVA radiation dose was applied consistently, following the principle of the original COLIPA test.

Main Results:

• Strong, significant correlations (Pearson correlation > 0.9) were observed between in vitro and in vivo UVAPF for both plate types.
• Higher UVAPF values and improved accuracy (regression slope of 1.05) were achieved using high-roughness plates compared to low-roughness plates (slope 0.83).
• Reproducibility between laboratories was comparable, with COV of 8% for low-roughness and 12% for high-roughness plates.

Conclusions:

• High-roughness plates significantly improve the accuracy of in vitro UVAPF determination compared to low-roughness plates.
• The high-roughness plate is recommended for the COLIPA UVA in vitro Test to enhance accuracy and minimize result variability.
• Optimized in vitro testing conditions, particularly plate surface, are vital for reliable prediction of in vivo UVA protection.