154 7O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 60 -- 50 -- 40 -- 30 -- 20 -- lO 1.30 A/[] 0 WATER 1.40 1.50 1.60.: :•:. '- REFRACTIVE INDEX Figure 9- The effect of refractive index on light transmission The hydration studies indicate that water acts on stratum corneum in at least ways to increase light transmission. The first is a result of liquid water which acts on the. ?•! surface to reduce light reflection and scattering. The second occurs as a result tion during which water is taken up by the cells and intercellular material causing a re•,:! i duction in internal scattering due to multiple changes in refractive index at the inter•:?i

PENETRATION OF LIGHT THROUGH STRATUM CORNEUM 00 135 90 Guinea pig in ethyl benzoate 80 Human sunburn 22u Everett 12 7O 60 5O 4O Human cantharidin lop Everett 12 o o 30 20 lO 300 400 500 WAVELENGTH,nm I•igure 10. Light transmission through human and guinea pig stratum corneum. Typical means and standard deviations are shown by the points and brackets, respectively

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