A New Sun Protection Factor Equation-Integrating Erythemal and Photoaging Risks across Biological and Space UV Exposure

This article proposes a novel formula for determining the Sun Protection Factor (SPF) of topical sunscreens by extending the classical spectrophotometric model. Unlike the traditional Mansur equation, which focuses on UVB radiation, this method is widely accepted for in vitro SPF determination, it has notable limitations. Primarily, it focuses solely on UVB radiation, neglecting UVA rays that penetrate deeper into the skin and contribute significantly to photoaging and carcinogenesis. The new model incorporates a broader ultraviolet spectrum (290–400 nm) and introduces an improved weighting function to represent both erythemal and photoaging risks. This method enhances SPF accuracy and aligns more closely with real-world exposure.