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j. Soc. Cosmet. Chem., 38, 321-331 (September/October 1987) Measurement of turnover time of stratum corneum using dansyl chloride fluorescence MOTOJI TAKAHASHI, YASUHIKO MACHIDA, and RONALD MARKS, Shiseido Laboratories, 1050 Nippa-cho, Kohoku-ku, Yokohama, Japan 223 (M. T., Y.M.), and Department of Medicine, University of Wales College of Medicine, Cardiff, CF4 4XN, UK (R.M.). Received January 27, 1987. Synopsis The change in turnover time of stratum corneum with age and circadian rhythm was examined using new instruments, a comparator and a fluorometer, to quantitatively assess skin fluorescence due to applied dansyl chloride. The effects of skin protection and keratolytic agents on turnover time were also studied. In two groups of 8 males ages 21-28 years and 6 males between 33 and 46 years of age, stratum corneum renewal times were 12.9 days and 15.1 days, respectively, suggesting that turnover time was prolonged with age. This study demonstrated that the rate of desquamation was considerably reduced in protected sites compared to normal unprotected sites. Furthermore, by taking readings twice daily it was found that the rate of dansyl chloride clearance was twice as fast in the daytime (9 AM-6 PM) as in the nighttime (6 PM-9 AM). The rate of desquamation was accelerated by keratolytic or inflammatory agents, especially salicylic acid. This technique may prove to be very useful to assess the efficacy of cosmetics and drugs. INTRODUCTION It is significant to study functional or structural changes of the skin due to aging for development of suitable cosmetics for different aged persons. However, most testing procedures for skin aging require biopsies or some other surgical manipulation, and simple, noninvasive methods are rarely used. Recently, the dansyl chloride (DC) fluorescence method has been used in dermatology for determination of stratum corneum renewal time (1-4), which can measure turnover time conveniently and noninvasively. The turnover time of stratum corneum is a useful parameter for dermatologists and cosmetic chemists because it is important for epi- dermal cell kinetic considerations and to investigate the effects of cosmetics or drugs on the epidermal metabolic rate. However, in previous work which used dansyl chloride, the end point of turnover time can be difficult to determine because of purely subjective visual methods. 321