280 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in three aspects: 1) water content of the skin surface before and after application of moisturizers 2) hygroscopicity, maximum water-holding ability of particular agents after hydrating the skin surface and 3) water-holding capacity, an ability to hold water on the skin surface after a single application of water by measuring the electrical conductance that should correlate with the amount of water on the skin surface. In this study, we used moisturizers available at the Institute of Dermatology, Bangkok, Thailand. The agents are cream base, 10% urea cream, 5% lactic acid cream, and pH5-Eucerin lotion, a commercial moisturizer, which contained Eucerit or lanolin alcohol. MATERIALS AND METHODS INSTRUMENTS This study used a skin surface hygrometer model Skicon 200 (IBS Inc., Hamamatsu, Japan), which reads the conductance in terms of •zS (microsiemen), which is the recip- rocal value of an ohm (fl). 1 S = 1 fl-1 In our procedure, we measured the conductance of the skin surface in three parts (Figure 1). First we measured the water content of the skin, before water application. This parameter was called the prehydration state or baseline level. Then we applied water on the skin for ten seconds, wiped it with tissue, and immediately measured the conduc- tance of the skin again. This parameter relates to the maximum water content that the skin can hold, called hygroscopicity. Consequently, we measured the conductance of the skin at 30-second intervals for three minutes. The pattern of conductance was called 1400 1200 1000 800 600 400 200 0 Microsiemen t.,,,•.S ) Water / • • Hold•"n½ .... pp. c lO sec. • 0 30 60 90 oereh ydrcrtion S e c o n d State 120 150 180 --•--Skin Water Content Figure t. Standard pattern measured by Skicon 200.

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