OPTICAL DISCRIMINATION OF SKIN 127 Figure 1C eter. Contour A is a diffuse reflection spectrum typical of those published in the litera- ture (14). Reflection is highest in the near infrared and red, i.e., 700 nm to 600 nm. The rapid fall between 600 nm and 400 nm is characteristic of absorption by hemo- globin with a doublet between 600 nm and 500 nm and the Soret band near 420 nm. Contour B, the polarized reflection spectrum, shows a completely different wavelength dependence, with very little contribution from hemoglobin and no appreciable change in the level of reflection from the far red (70%) to the violet (60%). The inflections near 570 nm and at 425 nm are probably hemoglobin, but the bands at 500 nm and 460 nm are new. The latter may, however, be present as a slight inflection in contour A. Figure 3 is representative of the polarized reflection spectra from the hand using the Jobin-Yvon spectrofluorimeter in synchronous scan mode. Contour A was obtained with polarizer and analyser perpendicular and is the depolarized reflection spectrum. The major attenuations of the reflected light are again attributable to hemoglobin. In the polarized reflection spectrum (contour B), the overall level of reflected light inten-

128 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS z o too õo B , I • I , 400 500 600 700 WAVELENGTH (NM) Figure 2. In vivo reflectance spectra of skin: A) Using an unmodified integrating sphere. B) Using an integrating sphere with a polaroid filter on the sample port. sity is up (88% relative to 77% in A) and the attenuation by hemoglobin absorption is down (allowing only 32% reflection in A and 48% reflection in B). In this case, how- ever, the contribution from the latter still dominates the spectral contour, unlike the equivalent spectrum in Figure 2. Contour C is the difference between A and B. The relative reflection difference is about 10% from 700 nm to 530 nm. The minima of about 5 % at 620 nm and 600 nm give the impression that a small inverted hemoglobin spectrum contributes between 500 nm and 600 nm with the Soret band at 430 nm. This is superimposed on a small reflection continuum from 700 nm to 400 nm. DISCUSSION It is unfortunate that in subjective assessments of the clinical condition of skin, it is often the subtle spadally dependent changes that supply the necessary information. The •.00. B z 0 50- • m C ' I , I • 400 500 600 700 WAVELENGTH (NH} Figure 3. In vivo reflectance spectra of skin using a synchronously scanning spectrofluorimeter: A) Po- laroid filters are perpendicular in the incident and reflected light beams. B) Polaroid filters are parallel in the incident and reflected light beams. C) (B)--(A) Difference spectrum.