376 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 80• 70- 60- (n 50-• --•40- 30- 20- 10- • 0 10 20 30 40 50 60 Time(min) Figure 8. Effects on phase-delay readings from skin treated with water (O) and 15% glycerol solution (A). The broken line shows the pretreatment value. Mean values + S.E. are given for each data point (n = 5). COEFFICIENT OF FRICTION Untreated forearm skin which had equilibrated with the environment was found to have a coefficient of friction of kt = 0.20 _ 0.01 (S. E.). Topically applied water showed a marked effect. A mean peak value of kt = 0.75 - 0.09 (S. E.) was observed between two and five minutes after treatment (Figure 6), after which friction fell within ten minutes to the pretreatment value. Application of 15 % aqueous glycerol (Figure 6) gave a similar mean peak friction value, kt = 0.68 - 0.04 (S.E.), after a short lubrication period (15 minutes). Elevated readings were recorded for periods in excess of two hours.

GLYCEROL TREATMENT OF SKIN 377 80- 70- 60- 20- 10- 0- I I • • • I • I I I • I 0 10 20 30 40 50 60 70 80 90 120 Time (min) Figure 9. Comparison of the efficacy of an oil-in-water lotion containing 15% glycerol (I) and the base lotion without glycerol (O) using the phase delay meter. The broken line shows the pretreatment value. Mean values + S.E. are given for each data point (n = 5). ELECTRICAL IMPEDANCE Figure 7 shows the increased readings of the phase delay meter on normal untreated skin equilibrated at high relative humidity levels in vivo. As the relative humidity of the atmosphere increased, the water content of the stratum corneum in equilbrium with it also increased, causing the phase delay reading to rise. These data are consistent with those of Blank (18) for the water content of stratum corneum between 20 and 95% relative humidity. At ambient temperature and humidity untreated forearm skin gave a mean phase delay value of 4.0 + 0.3 ! (S. E.) IXS. Topically applied water resulted in initially high values which dropped rapidly to the pretreatment value within ten minutes as the applied water evaporated (Figure 8). Skin treated with aqueous glycerol solutions or emulsions containing glycerol also showed the initial peak due to water (Figures 8 and 9), but the instrument continued to show elevated readings for at least two hours. PHOTOGRAPHIC ASSESSMENTS Expert assessment of the before-and-after-treatment photographs of each subject showed that the base lotion without glycerol had no statistically significant effect on overall hand skin condition (Figure 10) approximately one third of the subjects improved, one third became worse, and the remainder showed no change. The glycerol-containing lotion, however, improved the skin condition of 80% of subjects after one week's use (p