SPECTROSCOPIC STUDIES OF SKIN 471 RESULTS AND DISCUSSION The ATR spectrum shown in Fig. 2(a) was typical of those obtained from skin in situ. Its main features, which agreed with those reported by Blout and Mellors (1) for various tissues, are:- (i) the broad absorption centred at ca. 3400 cm-1 due to moisture, which probably obscured any absorptions due to NH groupings, (ii) the relatively weak C-H absorptions at 2950 and 2860 cm-1, (iii) the very weak carbonyl absorption at 1740 cm-l, due to an ester, (iv) the strong absorption at 1640 cm-•, which was due to a combination of a moisture absorption and the polypeptide amide Figure 2 ATR spectra of skin. I absorption, (v) the polypeptide amide II absorption at ca 1540 cm-•, and (vi) absorptions due to CH 2 and CH 3 groups at 1460 and 1380 cm-•. There were relatively small differences in the ratios of the intensities of the absorptions in the wavelength range 1300 to 1000 cm-• for different individuals and a very significant difference in the intensity of the moisture absorption at ca. 3400 cm-1. This latter effect was probably due to varia- tions in the perspiration rate between individuals the former variations have not been investigated further. The spectrum shown in Fig. 2(b) is of the same hand after a hand cream, the major components of which were mineral oil, fatty alcohol, water and stearic acid, had been applied in the usual manner. Comparison of this spectrum with that shown in Fig. 2(a) shows a very significant increase in the intensities of the absorptions at 2950, 2860, 1460 and 1380 cm-•. These absorptions are due to an aliphatic hydrocarbon grouping and the increased intensities indicated retention of the mineral oils and fatty alcohol by the

472 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS skin. There was also the appearance of a weak absorption at 1720 cm-1 in Fig. 2(b) which was due to the retention of the stearic acid. At the same time there was a marked decrease in the intensity of the moisture absorption at ca 3400 cm-1. This indicated a fall in the moisture content of the surface of the skin, probably due to the cream exerting a barrier effect. From Fig. 2(c) it can be seen that after the hand was washed with soap and water and dried, traces of the cream were still retained by the skin. This is shown by the persistence of the absorptions at 1720, 1460, 1380 and 1010 cm- 1. These results show that the retention of relatively major components of a product by the skin can be demonstrated by this technique. The degree to which a component can be detected depends, of course, on the actual intensities of the component's infrared absorptions. It should be pointed out that when the retention of a component has been shown it is not known whether the component is actually on the surface of the skin or absorbed into the surface layers. From previous studies it is known, however, that the depth of sample from which ATR spectra are obtained is of the order of a few microns. (Received: 22nd May 1967) •EFERENCES (1) Blout, E. R. and Mellors, R. C. Science 110 137 (1949). (2) May, L. and Grenell, R. G. Ann. N.Y. Acad. Sci., 69 171 (1957). (3) Schwarz, H. P., Appl. Spectry., 6 15 (1952). (4) Scheuplein, R. J., J. Soc. Cosmetic Chemists, 15 111 (1964). {5) Fahrenfort, J., Spectrochim. Acta, 17 698 (1961). {6) Hermann, T. S., Anal. Biochem., 12 406 (1965). (7) Ilarrick, N.J., Anal. Chem., 86 188 (1964).