304 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS implanted devices. The invasive techniques for placement and removal of collecting receptacles have serious drawbacks when the applicability of the results to mild skin wounds, producing tiny amounts of exudates, are to be considered. The internal reflec- tion, infrared spectroscopic method presented here, supplemented by contact angle measurements of surface properties, and further supplemented by measurements of ellipsometric and electronic parameters for these exudates (! 3, 31), should prove more useful because of the noninvasive character, nondestructive analysis and exceptional sensitivity to thin films of this method. DISCUSSION There is an important departure in the internal reflection, infrared method described here from the normal practice of this technique in other analytical fields. This is the utilization of internal reflection elements in a horizontal position to allow comfortable, gravitationally aided rather than hindered, skin analysis. Horizontal prisms also allow the fascile analysis of fluids, creams and/or medicinal preparations, which would drain from vertical surfaces. This departure from standard methods is not without some sacrifice. Figure 12 demonstrates, for example, the different baselines obtained for the same internal reflection prism mounted in a standard vertical mirror unit vs. the hori- zontal mirror unit preferred for cosmetic and wound-healing studies. The "baseline" quality for the simpler vertical mounting unit is considerably flatter and spectroscopi- cally more desirable than that for the horizontal device. The extreme, concave down, skewing of the baseline for the horizontal device is a disadvantage that must be ac- cepted in order to avoid more serious difficulties experienced when a volunteer is asked to hold a skin surface, with constant pressure, against the vertical face of an internal reflection prism or when drainage causes redistribution of a cosmetic prepara- tion on the prism face during analysis. Nevertheless, there are numerous circumstances in which the simpler setup and supe- rior baseline of the more standard internal reflection, spectroscopic devices may be ac- commodated to the needs of cosmetic or dermatologic analyses. As an example, the rapid analysis of wound fluid components collected in the crevice between shear- separated epidermal layers of friction blisters may be accomplished by first evaporating the fluid to dryness on a horizontal prism face and then turning the prism 90 ø for mounting in a standard vertical unit. Figure 13 presents an internal reflection infrared spectrum of the essentially pure proteinaceous components present in the fluid beneath such a friction blister on human skin and compares it with the spectral baseline for the clean prism in a vertical mounting device. Although friction blisters are very common causes of civilian and military disabilities, they have received very little scientific attention (22). Perhaps the availability of the simple analytical technique described here will allow their more careful examination and the development of improved wound dressings for their more rapid healing. Finally it must be noted that as cosmetic and medicinal preparations begin to incorpo- rate more natural products, and especially products of proteinaceous origin (23), the differentiation among natural skin, damaged skin and the proteinaceous ingredients of various cosmetics, salves, or ointments will become a great deal more difficult than has been the evaluation of cosmetic or therapeutic agents of predominantly hydrocarbon composition. In the former cases, it will be necessary to resort to refinements in the

CHARACTERIZATION OF HUMAN SKIN CHEMISTRY 305 J FREQUENCY (CM ) 4000 3600 3900 2800 2400 2000 1800 1600 1400 1200 1000 800 650 100 90 80 •6o z 1=5o •4o s.-- 30 20 10 0 i Figure 13. Internal reflection infrared spectra of clean germanium prism and of same prism coated with fil/• formed by fluid from beneath a friction blister on human skin. internal reflection spectral analyses, including attention to the specific locations and po: larizations of the protein absorption bands, and to specific features of contact angle data plots, which have been described elsewhere (24, 25). REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (12) (13) (14) (15) (16) c. H. March and A. A. Fisher, "Cutaneous Reactions to Cosmetics," Committee on Cutaneous Health and Cosmetics, American Medical Association, Chicago, Illinois, 1965. H. Bishop, Cosmetics are still not good enough!, The Chemist, 99 (March 1972). S. M. Wolfe, "Testimony Before the Senate Health Subcommittee Hearings On Cosmetic Safety," Publication # 156, Health Research Group, Washington, D.C., 1974. Anonymous, Poly-NAG helps healing, Chem. Eng. News, 13 (1971). H. I. Maibach and D. T. Rovee, Eds., "Epidermal Wound Healing," Year Book Medical Publishers Inc., Chicago, Illinois, 1972. G. Imokawa and T. Takeuchi, Surfactants and skin-roughness, Cosmetics and Toiletries, 91, 32 (1976). G. R. Berube, M. Messinger and M. Berdick, Measurement in vivo of transepidermal moisture loss, J. Soc. Cosmet. Chem., 22,361 (1971). W. A. Zisman, "Relation of the Equilibrium Contact Angie to Liquid and Solid Constitution," Ad- vances in Chemistry Series No. 43, American Chemical Society, Washington, D.C., 1964, pp 1-51. R. E. Baier, E.G. Shafrin and W. A. Zisman, Adhesion: mechanisms that assist or impede it, Science, 162, 1360 (1968). M. E. Ginn, C. M. Noyes and E. Jungermann, The contact angle of water on viable human skin, J. ColloidInterface Sci., 26, 146 (1968). N.J. Harrick, "Internal Reflection Spectroscopy," Interscience Publishers, New York, New York,, 1967. Available from Harrick Scientific Corporation, Croton Dam Road, Box 867, Ossining, NY 10562. R. E. Baier, "Applied Chemistry at Protein Interfaces," Advances in Chemistry Series No. 145, American Chemical Society, Washington, D.C., 1975, pp 1-25. F. Rijkens, "Organogermanium Compounds," Germanium Research Committee, Drukkerij eii Uit- geverij Schotanus & Jens, Utrecht, Holland (1960). A. E1-Shimi and E. D. Goddard, "Wetting of Keratin Substrates," in Advances in Chemistry Series No. 145, American Chemical Society, Washington, D.C., 1975, pp 141-154. R. E. Baier and W. A. Zisman, "Wetting Properties of Collagen and Gelatin Surfaces," in Advances in Chemistry Series No. 145, American Chemical Society, Washington, D.C., 1975, pp 155-174.