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j. Soc. Cosmet. Chem., 34, 263-271 (August 1983) In vivo percutaneous absorption of polyoxyethylene lauryl ether surfactants in hairless mice TOSHIO NISHIYAMA, YUHEI IWATA, KEISUKE NAKAJIMA, and TAKEO MITSUI, Shiseido Laboratories, 1050 Nippa- cho, Kouhoku- ku, Yokohama 223, Japan. Received October 28, 1982. Synopsis A quantitative method was used to determine the in vivo percutaneous absorption of •4C-lab•led polyoxyethylene lauryl ether (LAEO) surfactants in hairless mice. The amount of percutaneous absorption was determined by adding the amount retained in the body with the amount excreted in feces, urine, and expired air. The complete recovery of the applied dose was assured by employing a closed system for measuring the expiratory excretion. It was shown that the amount absorbed increased linearly with time. In the case of LAEO containing ethylene oxide units larger than 2 moles, the LAEO absorbed percutaneously was rapidly metabolized to CO• and excreted in expired air. Therefore, the rate of percutaneous absorption could be calculated from the rate of expiratory excretion. This result coincided with the amount obtained from the slope of the percutaneous absorption curve as a function of time. INTRODUCTION Since cosmetic products are applied directly on human skin, it is valuable to know the extent of percutaneous absorption of such materials. There are, surprisingly, only a few reports (1-5) on the percutaneous absorption of' oily ingredients, surfactants, and humectants used in cosmetics. Percutaneous absorption can be studied by in vitro methods using excised skin or by in vivo methods using live animals or subjects. In vitro percutaneous absorption has been investigated in detail in a series of studies by Scheuplein et al. (6-7) and by other researchers (8-10). Many reports have been made of in vivo experiments (11-14) of percutaneous absorption related to the content of materials in blood, urine, feces, and tissue. Various species of animals have been employed as a model of human skin in conventional experiments on percutaneous absorption. The present study attempts to quantify the percutaneous absorption in vivo of a series of non-ionic surfactants in hairless mice. The choice of this animal was based on two factors: (a) the hairless mouse does not require pretreatments such as shaving and depilation (b) Stoughton (16) has reported good agreement between hairless mouse skin and human skin in his percutaneous study of germicides, steroids, etc. 263