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On Photo-Stability of Oxybenzone

      To the Editor:
      I refer to a paper by
      • Schallreuter K.U.
      • Wood J.M.
      • Farwell D.W.
      • Moore J.
      • Edwards H.G.M.
      Oxybenzone oxidatiuon following solar irradiation of skin: photoprotection versus antioxidant inactivation.
      entitled “Oxybenzone oxidation following solar irradiation of skin: photoprotection versus antioxidant inactivation” that was published in the March issue of Journal of Investigative Dermatology. In this paper it is suggested that oxybenzone (2-hydroxy-4-methoxy benzophenone) is unstable to sunlight: there is a significant increase of the CO group concentration indicative of the oxidation of oxybenzone to its semiquinone. This conclusion encouraged us to perform some investigation by Fourier Transform Infrared Spectroscopy (FTIR) on the stability to light of oxybenzone.
      An acetone solution of the product was deposited on sodium chloride windows and on a KRS-5 crystal. The solvent was evaporated and a very thin layer of the product obtained. The layer on the crystal was exposed to sunlight for 2 h and the layer on the sodium choride windows was exposed to light in a Suntest CPS+ apparatus (Xenotest GmbH, Hanau, D) for 15 h. The multiple internal reflectance FTIR spectrum of the layer on the crystal and the transmission FTIR spectrum of the layer on the sodium chloride windows were recorded, before and after exposure to light, on a P.E. System 2000 instument (Perkin Elmer, Beaconsfield, U.K.).
      In both cases no change in the intensities of the carbonyl stretching bands or other changes in the IR spectrum were observed; Fig 1 shows the transmission FTIR spectra (i) before and (ii) after exposure to light.
      Figure thumbnail gr1
      Figure 1Oxybenzone on NaCl windows, FTIR spectra before (1) and after (2) exposure to light (15 h, Suntest CPS+, Xenon test, 500 Watt per m2).
      Both experiments show that oxybenzone is very stable under light and no significant semiquinone is generated.
      Finally, if Fig 1 of
      • Schallreuter K.U.
      • Wood J.M.
      • Farwell D.W.
      • Moore J.
      • Edwards H.G.M.
      Oxybenzone oxidatiuon following solar irradiation of skin: photoprotection versus antioxidant inactivation.
      is considered it seems that oxybenzone itself is absent in the Sultan facial cream as many of the oxybenzone absorbances are not present in the FT Raman spectrum of the cream. This observation, together with the results of our investigation, lead us to suspect that the study described in the paper has not been performed on oxybenzone, but on some other product.

      References

        • Schallreuter K.U.
        • Wood J.M.
        • Farwell D.W.
        • Moore J.
        • Edwards H.G.M.
        Oxybenzone oxidatiuon following solar irradiation of skin: photoprotection versus antioxidant inactivation.
        J Invest Dermatol. 1996; 106: 583-586