Why Skin Still Ages Under Sunscreen: SPF Mistakes That Leave You Exposed

The SPF number on a sunscreen bottle is frequently treated as a comprehensive rating of protection, but it measures a narrow metric: the time it takes for skin to burn compared to unprotected skin. This coefficient applies exclusively to UVB rays, the specific wavelength responsible for erythema (redness). The Spectral Gap: UVB vs. UVA Ultraviolet radiation is not uniform. While UVB rays damage the surface, UVA rays penetrate deeper into the dermis. UVA is the primary driver of photoaging, collagen degradation, and hyperpigmentation. Blocking one does not stop the other; therefore, a "broad spectrum" designation is the only way to ensure protection against both types of radiation. Formulation Analysis The actual performance of a sunscreen depends on how the filters and stabilizers interact within the formula: