Investigation on the Validity of in vitro Sun Protection Factor and Ultraviolet-A Protection Factor Evaluation Method...

Area of Science:

• Dermatology
• Photoprotection
• Analytical Chemistry

Background:

• The ISO24443 standard provides a method for in vitro determination of sunscreen protection.
• Ensuring the reliability and validity of this method is crucial for accurate product labeling and consumer safety.
• Previous studies have highlighted potential variability in in vitro sunscreen testing.

Purpose of the Study:

• To analyze factors influencing in vitro Sun Protection Factor (SPF) and Ultraviolet-A Protection Factor (UVA-PF) measurements.
• To verify the validity and reliability of the ISO24443 evaluation method for sunscreens.
• To identify sources of variability in in vitro SPF and UVA-PF determinations.

Main Methods:

• In vitro measurements of UV absorbance using various spectrophotometers.
• Comparison of SPF and UVA-PF results obtained with different spectral irradiance sources, including European Cosmetic and Perfumery Association (Colipa) 1994 and UV-solar simulated radiation (UV-SSR).
• Analysis of the impact of spectrophotometer differences and spectral irradiance on calculated SPF and UVA-PF values.

Main Results:

• UV absorbance measurements showed minimal differences across different spectrophotometers, even with significant absorbance variations above 2.
• In vitro SPF and UVA-PF values exhibited considerable differences when using Colipa 1994 or UV-SSR spectral irradiance.
• The necessity for re-evaluating the appropriateness of the coefficient of adjustment for in vitro UVA-PF determination was indicated.

Conclusions:

• The ISO24443 method demonstrates good reliability concerning spectrophotometer variability for in vitro SPF and UVA-PF.
• Spectral irradiance sources are a critical factor influencing the accuracy of in vitro SPF and UVA-PF results.
• Further investigation into adjustment coefficients is recommended for precise in vitro UVA-PF assessment.