94 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS SUMMARY AND CONCLUSIONS A hypothesis is presented that explains a wide variety of experimental observations regarding the adsorption of conditioning agents to keratin fiber surfaces. This hypoth- esis suggests that the adsorption of conditioning agents to hair should be considered as a continuum between a charge-driven process and a hydrophobically driven process. The exact nature of the reaction depends primarily on the structure of the adsorbing species and the pH of the system. The adsorption of species and systems to hair can all be explained on the basis of this hypothesis: increasing adsorption with increasing alkyl chain length for cationic surfac- rants (at acid pH) increasing adsorption of lipid/cationic with increasing lipid to cationic in formulated hair conditioners increasing adsorption with decreasing charge density for amodimethicones in an anionic surfactant medium and hydrocarbon adsorp- tion in an anionic medium. Changes in the wettability of keratin surfaces by an anionic dye (Orange II) and a cationic surfactant (CTAC) caused by pH changes above and below the isoelectric point of hair are also explained by this same hypothesis. REFERENCES (1) G. V. Scott, C. R. Robbins, and J. D. Barnhurst, Sorption of quaternary ammonium surfactants by human hair, J. Soc. Cosmet. Chem., 20, 135-152 (1969). (2) J. Steinhardt and E. M. Zaiser, Combination of wool protein with cations and hydroxyl ions, J. Biol. Chem., 183, 789-802 (1950). (3) G. Reese, Adsorption of amines on hair keratin, Fette Seifen Anstrichmittel, 68, 763-765 (1966). (4) R. Y. Lockhead, Conditioning shampoos, Soap Cosmetics Chemical Specialties, 42-49 (October 1992). (5) J. Steinhardt, C. H. Fugitt, and M. Harris, Further investigations of the affinities of anions of strong acids for wool protein, J. Res. Natl. Bur. Stand., 28, 201-216 (1942). (6) C. Robbins, Mechanisms for adsorption to keratins, Proceedings of the 8th Int. Hair Sci. Syrup., Kiel, Germany, September 1992. (7) C. R. Robbins, in Chemical and Physical Behavior of Human Hair, 2nd ed. (Springer-Verlag, New York, Berlin, 1988), p. 157. (8) C. R. Robbins, C. Reich, and J. Clarke, Dyestaining and the removal of cationics from keratin: The structure and the influence of the washing anion, J. Soc. Cosmet. Chem., 40, 205-214 (1989). (9) G. Kohl and E. G. Gooch, Method to determine silicones on human hair by atomic absorption spectroscopy, J. Soc. Cosmet. Chem., 39, 383-392 (1988). (10) T. Vickerstaff, in The Physical Chemistry ofDyeing, 2nd ed. (Interscience, New York, 1954), p. 413. (11) B. W. Barry and G. M. Saunders, The self-bodying action of the mixed emulsifier cetrimide/ cetostearyl alcohol, J. Colloid Interface Sci., 34, 300-315 (1970). (12) B. W. Barry and G. M. Saunders, The influence of temperature on the theology of systems containing alkyltrimethylammonium bromides/cetostearyl alcohol: Variation with quaternary chain length, J. ColloidInterface Sci., 36, 130-138 (1971).

j. Soc. Cosmet. Chem., 45, 95-107 (March/April 1994) The concept of sensory quality JO-ANN CLOSE, Close Associates, Route 5, Box 445, Rutherfordton, NC 28139. Received September 3, 1993. Presented at the Annual Scientific Seminar of the Society of Cosmetic Chemists, Baltimore, May 6-7, 1993. Synopsis Sensory evaluation is a growing discipline in the cosmetics and personal care products industry today. Having its roots in the food industry where most of the original methodology was developed, there are new challenges facing sensory scientists in applying these principles to skin care, hair care, fragrance, etc. Sensory analysis has been used successfully in new product development, product reformulation, stability, claims support, and competitive surveillance. It is critical that it now be applied to product quality. With the concept of total quality in the forefront thanks to the lessons Japan has taught us, it is essential that product sensory quality be monitored to fall within acceptable ranges based on consumer perceptions of product quality. Consumers, in fact, buy sensory quality and consistency. The first signals of product identity and performance are sensory signals--how the product they are about to purchase looks, feels, smells, etc. In companies where sensory performance is critical to product acceptance and efficacy, the margin of error for sensory quality is very small. As with all product development and support programs, sensory quality programs should be built upon consumer understanding--understanding how consumers define quality and what specific product parameters comprise it. INTRODUCTION In general business terms, a simple definition of quality is customer satisfaction. The concept of product quality is currently evolving from being expert-driven to being consumer-driven because a single expert opinion can rarely, if ever, consistently predict consumer acceptability in today's highly segmented marketplace. Yet many companies continue to rely on the N of 1! (1). Quality has also been described as the combination of attributes or characteristics of a product that has significance in determining the degree of acceptability of the product to the user (2). This necessarily means building in quality instead of putting it in after the fact. It means meeting consumers' expectations for a product consistently before shipment . . . every time. It means understanding how much deviation is tolerable before the product's sensory profile changes negatively in the eyes of the consumer. It means knowing how far to go given that the next batch of product will not always be identical to the last because raw materials and processes introduce unpredictable vari- ability. 95