THE GREASINESS OF MOISTURIZERS 181 cosmetic acceptability, as well as an impression of the absorbed amount, of a given moisturizer. The simple methodology studied in this paper reveals that it is possible to measure the non-absorbed moisturizer with an accuracy similar to that of other recog- nized biophysical methods. This approach therefore offers the possibility of studying actual absorption of moisturizers and other creams and subsequently better assessment of moisturizer efficacy per absorbed milligram. In addition, the quantification of non- absorbed residue on the skin surface has implications for the cosmetic acceptability of new preparations. ACKNOWLEDGMENTS The authors wish to thank Eva Hofmann, Ingelise Pealersen, Helle Thrane, and Bene- dicte Wulf for their excellent technical assistance. REFERENCES (1) C. Blichman, J. Serup, and A. Winther, Effects of a single application of a moisturiser: Evaporation of emulsion water, skin surface temperature, electrical conductance, electrical capacitance, and skin surface (emulsion) lipids, Acta Derva. Venerol. (Stockholm), 69, 327-330 (1989). (2) F. de Fine Olivarius, A. B. Hansen, T. Karlsmark, and H. C. Wulf. Water protective effect of barrier creams and moisturising creams: A new in vivo test method, Contact De•w•atitis, 35, 219-225 (1996). (3) R. Ghadially, L. Halki•er-S0rensen, and P.M. Elias, Effects of petrolatum on stratum corneum struc- ture and function,J. Am. Acad. Dermatol., 26, 387-396 (1992). (4) H. M. Brand and E. E. Brand-Garnys, Practical application of quantitative emolliency, Cosmet. Toiletr., 107, 93-99 (1992).

Cosmet. Sci., 49, 183-184 (May/June 1998) Book Review SKIN BARRIER, by Hans Schaefer and Thomas E. Redelmeier, 324 pages, Karger, Basel, 1996 (hard cover). This book is a comprehensive and up- to-date review of the field of percutaneous absorption, its relation to skin structure, and applications to product development and toxicology. The organization is logical and convenient. Drawing upon a wide range of authoritative sources, the current state of knowledge is summarized and, in some cases, interpreted. Researchers will find this volume a useful summary of the state of the art as well as a valuable key to the recent primary literature. The book is divided into six chapters, which begin with a description of the bio- logical underpinning of the skin's resis- tance to diffusion, go on to the relation between chemical structure and penetra- tion, penetration measurement and predic- tion, formulation and biological factors, and conclude with recommended measure- ment approaches. Each chapter begins with a brief introductory statement and ends with a summary of the main points. The references are collected in a single sec- tion at the end of the book. Many dia- grams and graphs illustrate the text. The first chapter, "Structure and Dy- namics of the Skin Barrier," reviews struc- ture and biochemistry, emphasizing the dynamic nature of the skin. The second chapter zeroes in on the makeup of the horny layer, examining in particular lipid composition and structure, as permeation is believed to occur chiefly via the inter- cellular lipid. The "brick-and-mortar" model is used as a basis for discussion. Various techniques used to obtain infor- mation on physical properties of the bar- rier membrane are described, along with the salient results. The next chapter describes the role of per- meant chemistry in percutaneous absorption and shows that there is a correlation with studies utilizing model membranes, such as liposomes. The evidence for the existence of functional pores in stratum corneum is presented. Some of the permeant variables discussed are octanol-water partition coef- ficients, ionization, and molecular weight. Methodology is the focus of the fourth chapter. The most relevant measurements, in vivo studies in humans, are discussed first. For various reasons it is often neces- sary to rely on in vivo data from animal studies or in vitro experiments utilizing ex- cised skin. Recommended protocols and the strengths and limitations of various techniques are discussed. In vitro penetra- tion experiments rely on the fact that the stratum corneum is the skin's primary bar- rier to penetration. They are the source of most of our current knowledge of the effect of vehicles and environmental variables on skin penetration. Next is a chapter on formulation and biological factors affecting percutaneous absorption. Practical matters affecting de- livery into the skin, such as evaporation and the in situ formation of supersaturated solutions, are included. The uses and drawbacks involved in penetration en- hancement by chemical agents are dis- 183