EVALUATION OF SKIN FRICTION 17 2 lOO 80 60 40 20 ß A ß B [] C A D ß E I I 5 10 15 Time, rain Figure 2. Sensory evaluation of the frictional resistance of the skin following application of five moistur- izing creams. The results are the mean from 11 panelists + S.D. s = Significantly different from cream B. evaluation (Figures ! and 2). The viscosity of the creams (see Materials and Methods) was lowest for cream A (5000 mPas) and highest for cream E (45,000 mPas). The instru- mental and sensory evaluations showed that cream E gave higher frictional resistance during application than did cream A (Figure 1 and 2). The panelists ranked the creams in the same order as could be expected from their viscosity (Figure 2, c.f. Materials and Methods). This indicates that during application of a cream, the frictional resistance depends on the viscosity of the product. Similar results have been reported following application of silicone oils to the skin (4). The consumer test also indicates that the creams differed in viscosity. The subjects preferred the application of cream B to that of cream E, which was considered to be too stiff (Figures 3 and 4). As water and other volatile agents evaporate, a marked rise in friction followed for the products, except for cream E. The area treated with cream E gave about the same resistance as did the untreated skin. The time course of the change in friction was almost the same for the two types of measurements. Product E gave the lowest friction and product A the highest. However, there was a tendency for the panelists to consider the friction to decrease after five minutes, whereas the instrumental measurements indicated a higher and more persistant friction after five minutes.

18 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS o 50 Cream A Cream B Cream E During After 15 application minutes Figure 3. Degree of liking of the perceived skin feel during application and 15 minutes following application of creams A, B, and E. The results are the mean from 15 subjects + S.D. * = Significantly different from cream B. In general, the intraindividual variation between the measurements was lower than the interindividual one, (Table I). However, the difference was not very high and consistent, suggesting that the surface topography of the skin and the possible presence of endog- enous substances on the surface had only a minor impact on the friction. The consumers rated the application of product B to be significantly more pleasant than the application of cream E (Figure 3). The consumers considered product A more slippery than product B at application (Figure 4). Fifteen minutes after application of the creams, the consumers rated the skin area treated with the cream B to be signifi- cantly more pleasant than the area treated with product E (Figure 3). This was explained by the individuals to be due to the slippery feeling of the latter area (Figure 5). This is probably due to the higher concentration of oils in that cream than in the other tested products. A large amount of nonabsorbed oil residue on the skin surface may give a lower friction. These findings support earlier observations concerning greasiness and skin friction (5). The more greasy and unpleasant the products were perceived as being, the lower the skin friction that was obtained (5). We have demonstrated significant differences in the influence on skin friction between the tested moisturizers, despite their similarities to a novice as oil-in-water emulsions.