WATER-HOLDING CAPACITY OF MOISTURIZERS 281 water-holding capacity. This value shows the ability of the skin to hold water in each time period. To obtain reliable results, we used the same probe and same examiner throughout the study. The examiner held the flexible cable that connects the probe with the machine, by the fingers, at about 10 cm distance from the probe, which was gently lowered on a test area to rest with its own weight (80 gm) on the skin without applying any additional manual pressure that could affect the result (7). SUBJECTS One hundred and eleven normal hospital personnel, from the Institute of Dermatology, Bangkok, male and female, ages 18--45 years, took part in this study. TEST AGENTS 1. Cream base (Institute formula) Formulation: Stearyl alcohol 7.00% Cetyl alcohol 2.67% Sodium lauryl sulfate 0.5% Liquid paraffin 18.0% Propylene glycol 6.67% Methyl paraben 0.02% Propyl paraben 0.0006% 2. 10% Urea cream (Institute formula) Formulation: Urea 10% W/W Cream base 3. 5 % Lactic acid cream (Institute formula) Formulation: Lactic acid 5% W/W Cream base 4. pH5-Eucerin lotion Formulation: Ammonium dihydrogen citrate 0.218 gm, ammonium monohydrogen citrate 0. 382 gm, in an oil-in-water emulsion containing Eucerit (lan- olin alcohol). METHODS In the examining room, a temperature of 24-26øC and a relative humidity of 45% was controlled throughout the study. To avoid sweating, subjects were asked to wait for at least five minutes before starting the examination. (The study was conducted in July 1991, and the average temperature was about 34øC in Bangkok after waiting, the subjects would feel cool and not sweat in the examining room.) The test procedure was divided into two parts: I. Prehydration state, hygroscopicity, and water-holding capacity of normal skin. We estab- lished a base level, or prehydration level, of the water content of the skin surface at the flexor surface of both forearms, 5 cm below the antecubital fossa, by taking three recordings and using an average result. After drops of water were applied to the exam- ination site for ten seconds and wiped off by tissue paper, conductance was measured

282 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS immediately after wiping, giving the maximum water content or hygroscopicity. Then the measurement was repeated at intervals of 30 seconds for three minutes, measuring water-holding capacity (7). 2. Prehydration state, hygroscopicity, and water-holding capacity on moisturizer-applied skin (immediate and delayed observation). We selected two square areas, 5 x 5 cm 2 each, at the middle part of both forearms the upper line of the square was 5 cm below the ante- cubital fossa. Using the syringe, we applied 10% urea cream on the first square of the left forearm, 2 •l/cm 2, and spread it evenly by a glass rod. After waiting five minutes, we observed an immediate result by measuring the water content of the prehydration state (baseline). Then we applied water for ten seconds and removed it carefully, trying not to remove the agent. Then hygroscopicity and water-holding capacity were mea- sured in the same manner as in the first test procedure. The same method was used to measure other agents: cream base was applied on another square area of the left forearm, and 5% lactic acid cream and pH5-Eucerin were applied on square areas of the right forearm. Prehydration state, hygroscopicity, and water-holding capacity were measured in the same manner (Figure 2). After that, we observed the delayed result by measuring the prehydration state, hygroscopicity, and water-holding capacity of all four agents three hours after application. STATISTICS The Kruskal-Wallis test and least significant difference (LSD) analysis were used to compare the results and analyze data. RESULTS There were 109 volunteers, 24 males and 85 females, ages 20-44 (average age, 30.96), who completed the experiment. Two women were excluded from the test because they were pregnant and hormonal changes might have interfered with the result. WATER CONTENT OF NORMAL SKIN We found that the prehydration state, hygroscopicity, and water-holding capacity of the normal skin of both forearms were approximately the same and did not have any statistical difference. The water content of the skin increased sharply after water appli- RIGHT LEFT Lactic aci .--Urea cream pHS-Eucerin Cream base Figure 2. Site of application of testing agents.