[Characterization of sun protection performance: Quo vadis?]

Area of Science:

• Dermatology
• Photobiology
• Cosmetic Science

Background:

• Early sunscreens aimed to prevent sunburn without hindering tanning.
• The need for quantifiable sun protection led to the development of the sun protection factor (SPF) test.
• The current SPF determination method (ISO 24444:2019) relies on UV radiation exposure to assess erythema.

Purpose of the Study:

• To evaluate the suitability of the current in vivo SPF determination method.
• To highlight the limitations of the existing SPF testing protocol.
• To introduce and advocate for alternative methods for SPF assessment.

Main Methods:

• Analysis of interlaboratory variability in current SPF testing.
• Comparison of SPF results using natural versus artificial sunlight.
• Review of alternative in vitro, hybrid diffuse reflectance spectroscopy (HDRS), and in silico methods.

Main Results:

• Significant interlaboratory variability exists despite standardized SPF testing.
• Artificial sunlight used in SPF determination yields significantly higher values than natural sunlight.
• Current SPF testing exposes subjects to potentially harmful UV radiation.

Conclusions:

• The current in vivo SPF determination method has significant limitations regarding accuracy and safety.
• Alternative methods like in vitro SPF, HDRS, and in silico calculations show promise for replacing the current standard.
• Immediate recommendations include reverting to descriptive protection levels (low, medium, high, very high) and future consideration of natural sunlight spectrum in SPF evaluation.