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J. $oc. Cosmet. Chem. 29 201-205 (1978) Effect of a skin cream containing the sodium salt of pifrollidone oarboxiflio acid on dry and flaky skin J. D. MIDDLETON* and MARESE E. ROBERTS Inveresk Research International, Edinburgh, EH21 7UB, Scotland Synopsis Humectants added to skin creams can increase the moisture retention of isolated stratum corneum and reduce the incidence of dry and flaky skin in vivo. This paper gives results of an investigation into the efficacy of a humectant, the sodium salt of pyrollidone carboxylic acid (Na PCA), which occurs naturally in the corneum. A product containing 5• of Na PCA increased the water-holding capacity of isolated animal comeurn. In a consumer trial, with assessment of skin dryness and flakiness by trained assessors, the Na PCA product was more effective than a control product containing no humectant and equally effective as a similar established product with a different humectant system. INTRODUCTION The integrity of the surface layer of skin, the stratum corneum, depends upon its ability to adapt without cracking to the forces applied during normal body movement. A lack of adequate flexibility and extensibility will result in corneum surface cracking and flaking, a condition commonly seen in dry and cold conditions on exposed skin. One factor of importance in maintaining corneum extensibility is its water content (1, 2). Many skin creams are, therefore, formulated with the objective of increasing the water content of the corneum. It is now well established (2-5) that an adequate corneum water content depends upon the presence within the corneum of hygroscopic water-soluble materials which can hold water in drying atmospheres. The water held by these hygroscopic substances is re- sponsible for much of the extensibility of the corneum (2). The hygroscopic water-soluble material within the corneum contains a mixture of substances (3). Amongst the more important hygroscopic components of the mixture are the sodium salt of 5-pyrollidone-2-carboxylic acid (Na PCA) (6) and lactate (3). Sodium lactate and lactic acid in a skin cream have been shown to be effective in increasing the water-holding capacity of isolated animal corneum and in reducing the incidence of dry and flaky skin as judged by trained assessors in consumer trials (7). This report gives an account of a similar investigation into the efficacy of Na PCA in a skin cream. EXPERIMENTAL MEASUREMENT OF WATER CONTENT OF ISOLATED CORNEUM IN HUMID ATMOSPHERES Corneum was obtained from the rear footpads of guinea pigs. It was separated by incubating the whole footpad in 0.1 mol tris buffer, pH 7'2, containing 2 tool urea and * Present address: Toxicol Laboratories, Bromyard Road, Ledbury, Herefordshire, HR8 1LG. 0037-9832/78/0400-0000 $02.00 ¸ 1978 Society of Cosmetic Chemists of Great Britain 201