204 J. D. Middleton and M. E. Roberts the greater water-holding capacity. Statistical analysis by Student's 't' test gave a value for 't' of 4.14 with 14 degrees of freedom indicating that the difference between creams was highly significant (P 0.001). Table I. Comparison of the effects of cream with and with- out 5•o Na PCA on water-holding capacity at 81% r.h. of solvent-damaged guinea pig footpad corneum Water held Cream (mg 100 mg -x dry corneum) With Na PCA 19 '4 (15) Without Na PCA 17.2 (15) Figures in brackets indicate number of replicates EFFECT ON HAND SKIN DRYNESS AND FLAKINESS IN A CONSUMER TRIAL One hundred and forty eight panellists completed the trial. Table H shows the mean total hand scores for all panellists in each of the six sequences and at each assessment. These figures show a considerable fluctuation of scores between sequences and assessments and the effects of creams are not easily distinguished. Table 1I. Mean total hand scores in consumer test for each product sequence at each assessment Cream No. of Assessment No. sequence panellists 1 2 3 4 abc 24 11.4 11.1 11-8 11.5 acb 24 12.7 14.1 10.6 15.3 bac 24 11.5 12.8 11.7 13.8 bca 23 11.2 13.4 12.2 13.5 cab 27 12.3 13.2 11.9 16.7 cba 26 12.5 13.8 14.9 15.6 a = cream with Na PCA. b = cream as (a) but without Na PCA. c = urea cream. Statistical analysis was carried out on the mean changes in total hand score for each cream. Table III shows the mean changes for each cream during each of the three use periods. The overall means for each period and for each cream are also given together with the difference between creams required for statistical significance. The statistical analysis showed that the cream containing 5•o Na PCA resulted in significantly lower hand scores, i.e. in better hand skin condition, than the control formu- lation containing no Na PCA There was no significant difference between the cream containing Na PCA and the cream containing urea. The urea cream resulted in a lower hand score than the control cream.

Effect of pyrollidone carboxylic acid 205 Table lII. Mean changes in total hand score in consumer trial for each cream during each period of use Period no. Cream Cream 1 2 3 mean a 0.5 -1.2 1.0 0.11 b 1.7 0.9 4.8 2.47 c 1.1 -2.3 0.9 -0.07 Period mean 1.1 - 0' 9 2.3 Difference between creams required for statistical significance (P=0.05)=1.56 a = cream with Na PCA b = cream as (a) but without Na PCA c = urea cream. DISCUSSION The results of the study on isolated animal corneum showed that the addition of 5•o Na PCA to a skin cream could result in a measurable increase in water-holding capacity of the corneum. In order to determine whether or not this increase in water content would be of any significance when the cream with Na PCA was used in the normal manner, the consumer trial was carried out. The consumer trial showed that the increased corneum water content did result in an improved hand skin condition as judged by trained assessors This improved skin con- dition caused by the Na PCA cream was equal to that resulting from the use of a cream coilraining urea. The results of these experiments, therefore, demonstrate that the presence of Na PCA in skin creams can reduce the incidence of dry and flaky skin under normal use conditions. REFERENCES 1 Kligman, A.M. In Montagna, W. and Lobitz, W. C. The Epidermis 410 (1964) (Academic Press, New York). 2 Middleton, J. D. The mechanism of water binding in stratum corneum. Brit. J. Dermatol. 80 437 (1968). 3 Speir, H. W. and Pascher, G. Zur analytischen und funktionellen Physiologie der Hautoberfl•iche. Hautarzt 7 55 (1956). 4 Blank, I. H. Factors which influence the water content of the stratum corneum. J. Invest. Derrnatol. 18 433 (1952). 5 Jacobi, O. K. About the mechanism of moisture regulation in the horny layer of the skin. Proc. Sci. Sect. Toilet Good Assoc. 31 22 (1959). 6 Laden, K. and Spitzer, R. J. Identification of a natural moisturising agent in skin. J. Soc. Cosmet. Chem. 18 351 (1967). 7 Middleton, J. D. Development of a skin cream designed to reduce dry and flaky skin. J. Soc. Cosmet. Chem. 25 519 (1974). 8 Gibson, I. M. The evaluation of hand-care preparations. J. Soc. Cosmet. Chem. 24 31 (1973).