j. Soc. Cosmet. Chem., 44, 279-288 (September/October 1993) Flygroscopicity and water-holding capacity of moisturizing agents: A single-application in vivo study JIROT SINDHVANANDA, PIMOLPUN GRITIYARANGSAN, PRAWIT RUNGRAIRATANAROIJ, and PREYA KULLAVANIJAYA, Institute of Dermatology, 420/7 Rajavithi Road, Phrayathai, Bangkok 10400, Thailand. Received November 18, 1992. Synopsis A comparative study of four kinds of moisturizers for their hygroscopicity and water-holding capacities as measured by a skin surface hygrometer showed that all agents could improve the water content of the skin surface. The most effective agent was Eucerit, a lanolin alcohol-containing agent, and the second was a urea-containing agent. The Eucerit-containing agent also showed high stability accoMing to the water- holding capacity patterns observed after five minutes and three hours. INTRODUCTION The water content of the stratum corneum plays an important role in providing the skin surface with suppleness, good function, pliability, and smoothness (1). This thin layer serves as a protective sheath that protects the body from the invasion of various kinds of external attacks (2) such as living organisms, chemical agents, and physical factors. There is a big difference between the moist and humid environment beneath the stratum corneum and the dry atmosphere outside the body, and the stratum corneum is the only layer between them. In vitro studies on stratum corneum showed that it is flexible as long as it contains more than 10% water (3). The water-holding property of the stratum corneum is influenced by water-soluble materials, such as free amino acids, organic acids, urea, and inorganic ions (4). Lipids in the lamellar structure in the intercellular spaces of the stratum corneum also play a part in water-holding (5,6). Smooth and soft skin is not only good-looking but is also healthy. On the other hand, dry, scaly, or rough skin shows an unhealthy condition or underlying disease (7) and reflects low water content in the stratum corneum (3). People accept these concepts and try to use agents to improve water content and smooth their skin. There are many agents on the market that claim to smooth the skin and hold water on the skin surface. A variety of techniques for assessing skin hydration have been developed and reviewed (7-11). Most in vivo techniques are based on electrical measurements such as resistance, capacitance, impedance and, conductance. We try to evaluate the moisturizing agents 279

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.