The effect of solvents on the ultraviolet absorbance of sunscreens

Synopsis The efficacy of sunscreens is often influenced by the solvents inwhich they are dissolved. In this regard, the ultraviolet (UV) absorption spectra of 13 UVA and UVB sunscreen chemicals were determined in 12 solvents ofvarying polarity and cosmetic interest. Changes inboth the wavelength of maximum absorbance (K max) and molar absorptivity (1⁄2) were observed for many of the sunscreen-solvent sys ems studied. Observed hypsochromic and bathochromic shifts in K max for a number of sunscreen chemicals were related to their structure and polarity. Polar solvents shifted the K max of polar sunscreens to shorter wavelengths (hypsochromic) andshifted less polar sunscreens to longer wavelengths (bathochromic). Ortho-substituted sunscreen chemicals, uch as salicylates and anthranilates xperienced a minimum or no UV absorbance shift.