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There are considerable data to suggest that protection from solar ultraviolet (UV) radiation will reduce the risk of acute and chronic skin damage in humans. Whereas the sun protection factor (SPF) provides an index of protection against erythemally effective solar UV, largely confined to the UVB (290-320 nm) and short-wavelength UVA (320-340 nm) region, there is currently no agreed-upon method to measure broad-spectrum protection against long-wavelength UVA (340-400 nm).

The objective of these studies was to assess the potential of in vitro UV substrate spectrophotometry and subsequent calculation of the “critical wavelength” value as a measure of broad-spectrum UV protection and as a routine, practical procedure for classification of sunscreen products.

The spectral absorption of 59 commercially available sunscreen products and multiple experimental formulas with one …