120 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 45 y = -0.37x + 46.6 • 40 * r = -0.86 • p 0.05 • * • 30 , o øo • ß • 25 •------- • o o •o ••o •1 20 y =-0.22x + 33.3 o d r = -0.82 15• P 0.05 (-//I • I 20 30 40 50 60 tge (:re ar.) Figure 5. Number of peaks (Rn) as a function of age of the volunteers. The upper line and the asterisks represent the scrubbed area and the lower line and circles the area before any treatment. smaller width than the surface of the plateaus. Thus, a negative value of the Rsk could be expected. The value is similar to that reported by others (11). Lowering of the Rsk may indicate that the scrubbing makes the plateaus more planar, possibly by the re- moval of large peaks. Rn and amplitude parameters might be used to describe the perceived differences be- tween rough and smooth skin. Dry skin is rough to the touch and characterized by a decrease in Rn (5,12) and an increase in amplitude parameters (5) compared to normal skin. Young skin is smoother than older skin, and data in the present study showed that Rn increases with decreasing age. The use of the scrub cream removed stratum corneum material from the skin, resulting in an increase in Rn and a decrease in the amplitude parameters. Thus, these findings are compatible with the perception of smoothness after using a scrub cream. ACKNOWLEDGMENTS We would like to thank Dr. Magnus Lindberg, Karolinska Institute, and Professor Bj6rn Lindeke, ACO AB, for their helpful criticism of the manuscript. REFERENCES (1) A. F. E1-Shimi, In vivo skin friction measurements,J. Soc. Cosmet. Chem., 28, 37-51 (1977).

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