12 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ACKNOWLEDGMENTS The authors thank Bohlin Rheologi and Schering-Plough for the use of rheometers Mr. Steve Colo of Bohlin Rheologi for helpful discussions and Mr. Ross Clark of Kelco, Mr. Peter Ciullo of R. T. Vanderbilt, and Dr. Michael Kopcha of Schering-Plough for reviewing the manuscript. REFERENCES (1) J. L. Zatz and S. Knapp, Viscosity of xanthan gum solutions at low shear rates, J. Pharm. Sci., 73, 468-471 (1984). (2) M. M. Santore and R. K. Prud'homme, Rheology of a xanthan broth at low stresses and strains, Carbohydrate Polym., 12, 329-335 (1990). (3) W. E. Rochefort and S. Middleman, Rheology of xanthan gum: Salt, temperature, and strain effects in oscillatory and steady shear experiments, J. Rheol., 31, 337-369 (1987). (4) J. L. Zatz and G. P. Kushla, "Gels," in Pharmaceutical Dosage Forms.' Disperse Systems, H. A. Lieher- man, M. M. Rieger, and G. S. Banker, Eds. (Marcel Dekker, New York, 1989), Vol. 2, pp. 495- 510. (5) P. A. Ciullo, Rheological properties of magnesium aluminum silicate/xanthan gum dispersions, J. Soc. Cosmet. Chem., 32, 275-285 (1981). (6) H. A. Barnes, J. F. Hutton, and K. Walters, An Introduction to Rheology (Elsevier, New York, 1989). (7) P. J. Whitcomb, B. J. Ek, and C. W. Macosko, Rheology of xanthan gum solutions, in Extracell. Microb. Polysaccharides Syrup., P. A. Sandford and A. Laskin, Eds. (ACS Symposium Series, Wash- ington, DC, 1977), Vol. 45, pp. 160-173. (8) J. L. Zatz and C. Yarus, Stabilization of sulfamerazine suspensions by xanthan gum, Pharm. Res., 3, 118-121 (1986). (9) J. L. Zatz and B. K. Ip, Stabilization of oil-in-water emulsions by gums, J. Soc. Cosmet. Chem., 37, 329-350 (1986).

j. Soc. Cosmet. Chem., 43, 13-20 (January/February 1992) Instrumental and sensory evaluation of the frictional response of the skin following a single application of five moisturizing creams MARIE LODI•N, H•KAN OLSSON, LIZBET SKARE, and TONY AXI•LL, ACO HUD AB, Research and Development, S-112 87 Stockholm, Sweden (M.L., L.S.), and Department of Oral Surgery and Oral Medicine, School of Dentistry, Carl Gustaft viig 34, S-214 21 Malmb', Sweden (H. 0., T.A. ). Received April 20, 1991. Synopsis Application of a cream to the skin induces tactile changes of the surface. The frictional characteristics of products are important in consumer acceptance. The frictional resistance following application of five moisturizing creams was studied using sensory analysis and a newly developed sliding friction instrument. The methods gave comparable results. During appli- cation of the products, an immediate reduction in friction was obtained, followed by a gradual increase. A urea-containing cream gave rise to high frictional values, whereas a cream containing a high concentration of oils gave low frictional values. Separate consumer tests showed different preferences due to the different behavior of the creams. Successful correlation between consumer tests and instrumental data would be a key to introducing new quantitative measures of product performance. INTRODUCTION In the cosmetic and pharmaceutical industries it is important to develop topical for- mulations that have maximum consumer and patient acceptability. Otherwise, the formulations will not be used, even if they have suitable biological effects. Application of products to the skin induces tactile and visual changes of the skin surface. Volatile compounds, such as water, evaporate, and the remaining constituents are mixed with other substances on the skin. For product attributes of creams, not only is the ratio between oil and water important, but also the type of oil as well as the amount and type of other ingredients (emulsifiers, humectants, etc.). The combination of substances influences the initial feel, how the formulation spreads on the skin, whether and how fast it is absorbed, and how the skin feels after use. To evaluate such product differences a variety of test methods are needed. Tactile perception involves a contact and a movement of a fingertip across the skin 13