MOISTURE MEASUREMENT BY NIR SPECTROSCOPY 257 600 c 550 500 450 400 350 300 m m m 1927 nm m m •/'m • m m m m .••m m m 1 ab$olufe humidify, g/m3 Figure 6. Correlation of bound water (1927 nm) and absolute humidity. 10 600- 400 t 8001 x 6001 4001 200! absolute humidity, g/m3 Figure 7. Correlation ooe bulk water (1890 nm) and absolute humidity. the epidermis dominates, with only 5%-7% diffuse reflectance. Light that does not penetrate into the SC can undergo single scattering or multiple internal scattering. The stratified nature of the stratum corneum, with its layers of flattened cells, provides several opportunities for internal scattering. Some light may also be completely absorbed

258 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 1 rear ß , treatment beforet•. treatmen 1•oo 16'00 ' 18'00 ' 20'00 nm Figure 8. Apparent absorbance spectra before and after product application. 60 i i i 40 20 -6O -80 1879 1890 1909 1927 wavelengfh (nm) Figure 9. Net concentration changes after product application. r 2200 into the deeper tissues. According to Scheuplein (14), IR radiation at the water absorp- tion bands that is not absorbed or scattered by the SC will be absorbed by the first few viable cell layers of the epidermis. Radiation that penetrates deeper into the skin is less likely to be returned to the surface and thus will not be measured.

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