GLYCEROL TREATMENT OF SKIN 371 54 53 52 51 5O 49 • 47 • 45 o '• 8- •: 7- 6- 5- 4- • 1 I I i I I I I I 0-02 I 2 3 4 5 6 7 Time (h) Figure 3. Effects of oil-in-water cream containing 10% glycerol (I) on transepidermal water loss (p 0.02 by comparison with the non-glycerol control cream (O), at all time points between one and seven hours, Student's paired t-test). The broken line shows the pretreatment value. Mean values -+ S.E. are given for each data point (n = 10). similar to a simple electric circuit (Figure 1). At a given frequency of applied alter- nating voltage it resembles a resistor (R•) and capacitor (C) connected in parallel. Water increases the capacitance of the outer layers of dry stratum corneum (15), and the increased plasticity of hydrated skin improves the electrical contact that an electrode makes when gently held by its own weight on the skin thus any instrument which measures the contact resistance, internal resistance, capacitance, or a combination of these parameters (impedance at a stated frequency) should detect an increased water content after hydration. In order to examine the electrical characteristics of the stratum corneum, a phase delay

372 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 30- :I, 20- E o 'o10_ 0 Ill 0 2 3 4 5 6 Time ( h ) Figure 4. Reduced skin surface roughness after topical treatment with water (O) (p 0.05 at ten minutes, Student's paired t-test), and 10% aqueous glycerol solution (i,), (p 0.02 at 30 minutes, one hour, and two hours, Student's paired t-test). The broken line describes the change in the roughness of untreated skin sites. Mean values _ S.E. are given for each data point (n = 6). meter which measured a combination of capacitance and resistance was used. The in- strument was developed in conjunction with the Torry Research Station (16). A 2 KHz signal was applied to the skin via a four-terminal device. The delay (in microseconds, }xs) between the applied voltage cycle and the cycle of current flow was measured. The increase in phase delay readings after treatment gave a measure of skin hydration.