ASSESSMENT OF SKIN CARE PRODUCTS 13 % 60 5O 4O 3O [] Product ,,N, ß Product Mean Value = 29,56 50,0 48,6 45,3 31,2 25,0 R 24,2 i i oii i 2,10 o I BA BDF Be He Ho Ma Na R SchrSchwWe Center X X X X X X X x = Centers which performed objective tests too 13,9 Mean Value: 31,06 50,0 24,4 22,2 20,0 17,2 12,5 9,7 BA BDF Be He Ho Ma Na R SchrSchw We X X X X X X X Figure 7. Change of skin surface, positive assessment. DGK multicenter study. CORRELATIONS The main objective of our study was to find out if a change in skin condition or an improvement in skin surface smoothness due to application of the creams could be perceived by the panelists, whether it could be measured by objective methods, and whether subjective assessments correlate with objective data. For comparisons between subjective and objective assessments, only those centers are taken into account that have performed both tests. In Figure 8, values for skin hydration expressed by efficacy values received by the corneometer method (see Table I) are compared with subjective assessed data. The good correlation is evident. Objective and subjective assessments parallel very well. Only at those centers where high hydrating efficacies were measured, high ratios of positive assessments of skin surface were also perceived by the panelists. Conversely, at those centers where only low increases in skin smoothness were perceived by the panelists, low efficacies were measured. Figure 9 shows the comparison of skin roughness reduction measured by means of methylene blue adsorption with subjective assessment of the panelists. The correlation for "K" is better than for "N," but less evident than for the corneometer method. As efficacy values for surfometry and image analysis are in a range between 5 and 10% and only two centers applied this method, we refrain from comparisons. DISCUSSION AND CONCLUSIONS The objectives of our study were comparisons of biophysical measurements with sub- jective assessments, comparisons of objective methods in different laboratories, and

14 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS [] Product ,•% after 4 weeks positive assessment [] Product ,•% after 4 weeks positive assessment A% 50 20 Be He R We Be He R We Be He R We Be He R We Center Figure 8. Correlations between skin hydration and positive assessments of skin by panelists. ,•% after 4 weeks .1'• Product positive assessment [] Product ,•% after 4 weeks positive assessment A% -40 - 30 - 20 o B BDF Schr Schw We Center BDF Schr Schw We I 5O 4O 3O IIII IIl,f lO i i i i i i i T 0 BDF Schr Schw We BDF Schr Schw We Figure 9. Correlation between skin roughness measured by means of methylene blue method and positive assessment of skin surface by panelists. assessment of the credibility of different methods. Most of the important German cosmetic scientists were represented in this task force, but each center had performed biophysical tests and subjective tests under different conditions till then. Therefore, the first step was to agree to standardized test methods. The chosen test creams have been well accepted on the German market for years. Both creams were results of long-term research and development and optimization by means of biophysical measurements and consumer tests. By choosing an oil-in-water and a