WATER-HOLDING CAPACITY OF MOISTURIZERS 285 1400 1200 1000 800 600 400 200 0 P = 0.05 5)2)4-3)1 •)4)3)1__ • 5)2)4.3) 5)2)4. 5)2) 0 30 60 90 120 150 180 sec. • CONTROL [1l [• 10% UREA [21 • CREAM BASE [3l • 5% LACTIC ACID [4]• pH5-Eucerin [5] Figure 5. Hygroscopicity and water-holding capacity pattern of observation three hours after application. cream base, and control normal skin were nearly the same at the prehydration state. After applying and wiping off water, pH5-Eucerin and 10% urea cream both showed the highest hygroscopicity, and both of them showed the same water content level at the beginning of the water-holding capacity period. But after one minute, pH5-Eucerin obtained higher efficacy than 10% urea cream (Figure 6). The water-holding capacity of all agents dropped faster than at five minutes after application (Figure 7), except for 1400 1200 1000 8OO 6OO 4OO 2OO 0 0 30 60 90 120 150 180 sec. lO% UREA CREAM •PH5-EUCERIN Figure 6. Comparison of results of 10% urea cream and pH5-Eucerin at observation three hours after application.

286 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS pH5-Eucerin, which retained the ability to hold water at nearly the same level. At 180 seconds, all agents still had water content levels higher than the normal skin control (Figure 5). DISCUSSION The water content of stratum corneum in our test is chiefly concerned with the amount of the rapidly gained and lost "bound water" in stratum corneum (12). The baseline conductivity of normal skin is around 180 MS, which is higher than in other reports (7). This could be due to the climate in Thailand, which is warm and humid. Normal skin has a high hygroscopicity but a low water-holding capacity, and water content drops sharply in 30-60 seconds. This experiment, like previous reports (13-18), showed that moisturizers can increase the water content of the prehydration state and improve water-holding capacity. Com- paring water content at the prehydration state at five minutes and three hours after application of moisturizers, we found that the water content of the latter is less than that of the former. There are many reasons to explain this event: perhaps the properties of the agents are not stable due to degradation, or when we wiped off water, part of the agents may have also been removed. pH5-Eucerin showed the highest water content, meaning that this agent is more stable and longer-lasting. We were disappointed that we could not continue the experiment longer than three hours because the volunteers were not available. This meant that we could not establish when the water content of all treat- ments dropped to the level of normal skin. Among these agents, pH5-Eucerin obtained the highest hygroscopicity, both at five 5% LACTIC ACID _.,•.S 14oo 1200r 1 1000 t • 120 lOO 600 60 4oo F - 4o =øøl ...... I =o o, • - '•o •o' ,'o -,•o 1•o 18o 8e½. •'- AFTER 5 MIN, • AFTER 3 HR. pH5-Eucerin 14øø/• 1200 I 1000 • 800 V 400• 0 30 60 90 120 sec, •'-- AFTER 5 MIN. • AFTER 3 HR. 10% UREA CREAM 0 30 60 90 120 150 180 -4-- AFTER 5 MIN. • AFTER 3 HR. CREAM BASE I // ,00?/ T ...... 150 180 0 30 60 90 120 150 180 SeC. •'-- AFTER õ MIN. • AFTER 3 HR. Figure 7. Hygroscopicity and water-holding capacity of all agents, comparing observations five minutes and three hours after application.