SOLVENTS AND SUNSCREEN ABSORBANCE 213 O-IC'-IC'-IC'-IC'-IC'-IC'-IC'-IC'-IC'-I _.[_ II 0000 + II

214 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Absorbance units Absorbance units -6.?62 • r•O 72? • t / '%,., •, // x,, 100% ETHYL ALCOHOL / \ /' I" \ / , ,, /' !, 588,8 Wavelepgth (rim} ! ! ! / / / i i ETHOXY ETHANOL Wavelength (rim) Figure 1. UV absorption spectra of PABA showing a hypsochromic shift in the •. max in the UVB region (290 to 320 nm) from a less polar solvent (ethoxy ethanol) to a more polar solvent (ethanol). tive lipophilicity, a measure of a compound's relative polarity, has been determined by calculating the log of the partition coefficient between octanol, a model lipid, and water (log P) for 15 sunscreen chemicals. These data are listed in decreasing order of polarity (i.e., increasing log P values) in Table V. The log P values were calculated from the structural formula of each sunscreen in accordance with Rekker's method of deter-