SKIN SMOOTHNESS AND SKIN SOFTNESS 103 410 4OO 390, 370 PRE LOTION WATER 350 PRE• 2 POST• TRIAL Figure 3. Skin softness in two groups treated prior to and following treatment with lotion or water Discussion.' Experiment I It is clear that soaking in water or applying a lotion has an immediate effect in enhanc- ing skin softness. After 5 min, however, the effect of the water had dropped significantly, whereas that of the lotion had remained. Apparently, the moisturization effect produced by the water had been dissipated in 5 min whereas that induced by the lotion lasted at least that long, as measured by this technique. MEASUREMENT OF COEFFICIENT OF FRICTION AS A METHOD OF DETERMINING SKIN SMOOTHNESS We applied the concept of the coefficient of friction in producing a device which assesses the smoothness of skin (Figures 4A and 4B). The device comprises a sled of deglazed thermoplastic drawn by a constant-speed (5 mm/min) motor. The force re- quired to move the sled over skin is measured by a force transducer the resultant voltages from the transducer are amplified and fed to a digital voltmeter, calibrated to read in grams. A rod with a small ball-bearing point rests constantly upon the sled, which is placed upon the area of skin to be tested. The skin and sled are kept hori- zontal. Measures of the maximum forces required to move the sled are continuously made and recorded. Several, e.g., ten, determinations can be made in the space of a few

104 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figures 4A and 4B. The device for assessing skin smoothness minutes and prove to be quite consistent for the same degrees of smoothness. The mean of the determinations is used as the index of smoothness. SKIN SMOOTHNESS: VALIDITY To assess the validity of the system, we employed five grades of sandpaper varying in roughness in grains per linear inch as follows (from rough to smooth): 320, 360, 400,