BROAD-SPECTRUM SUNSCREENS 15 5 repeated exposures to suberythemal doses of UVB and UVA in human skin, J. Am. Acad. Dermatol., 32, 53-62 (1995). (18) F. Urbach, Ultraviolet A transmission by modern sunscreens: Is there a real risk? Photodermatol. Photoimmunol., Photoreed., 9, 237-241 (1992/1993). (19) L. H. Kligman and IV[. Gebre, Biochemical changes in hairless mouse skin collagen after chronic exposure to UVA radiation, Photochem. Photobiol. 54, 233-237 (1991). (20) K. Scharffetter, IV[. Wlaschek, A. Hogg, K. Bolsen, A. Schothorst, G. Goerz, T. Krieg, and G. Plewig, UVA radiation induces collagenase in human dermal fibroblasts in vitro and in vivo, Arch. Dermatol. Res., 283, 506-511 (1991). (21) M. Wlaschek, K. Bolsen, G. Herrmann, A. Schwarz, F. Wilmroth, P. C. Heinrich, G. Goerz, and K. Scharffetter-Kochanek, UVA-induced autocrine stimulation of fibroblast-derived collagenase by IL-6: A possible mechanism in dermal photodamage?J. Invest. Dermatol., 101, 164-168 (1993). (22) P. Zheng and L. H. Kligman, UVA-induced ultrastructural changes in hairless mouse skin: A comparison to UVB-induced damage, J. Invest. Dermatol., 100, 194-199 (1993). (23) L. H. Kligman, "UVA-Induced Biochemical Changes in Hairless Mouse Skin Collagen: A Contrast to UVB Effects," in Biological Responses to Ultraviolet A Radiation, F. Urbach, Ed (Valdenmar Pub- lishing Co., Overland Park, KS, 1992), pp. 209-215.

j. Soc. Cosmet. Chem., 47, 157-166 (May/June) A natural lipid mixture improves barrier function and hydration in human and murine skin MAN MAO-QIANG, KENNETH R. FEINGOLD, FUSHENG WANG, CARL R. THORNFELDT, and PETER M. ELIAS, Dermatology and Medicine Services, Veterans Administration Medical Center, San Francisco, CA 94121 (M.M-Q., K.R.F., P.M.E.) Departments of Dermatology (M.M-Q., K.R.F., P. M. E. ) and Medicine (t•. if. t • . ), University of California School of Medicine, San Francisco, CA Department of Dermatology, Yuhuangding Hospital, Yantai, P. R. China (F. W. ) and Cellegy Pharmaceutical Corporation, Foster City, CA (C.R. T). Accepted for publication July 18, 1996. Synopsis Previous studies have demonstrated that three key lipids, cholesterol, free fatty acids, and ceramides, are required for maintenance of the epidermal permeability barrier function in murine and human epidermis. Moreover, it has been shown that all three lipids are required together for barrier function, because only topical applications of complete, equimolar three-component lipid mixtures allow normal barrier recovery in disrupted skin. In contrast, single- or two-component lipid mixtures delay normal barrier recovery. Furthermore, increasing the ratio of any single lipid species, i.e., cholesterol, ceramides, or free fatty acid, to the other two lipids in the three-lipid component mixture actually accelerates barrier recovery in murine and human epidermis. Here we assess whether a natural lipid mixture, containing these three key lipids in addition to a large amount of phospholipids, influences barrier recovery and skin hydration in both murine and human skin. Our results show that this natural lipid mixture enhances barrier recovery significantly in acetone-treated mouse skin. Moreover, this natural lipid mixture also accelerates barrier recovery in acetone- treated and tape-stripped human skin. Finally, this natural lipid mixture increases stratum corneum hydration in both acutely disrupted and normal human skin. These studies show that this naturally occurring lipid mixture can both accelerate permeability barrier recovery and enhance stratum corneum moisturization. INTRODUCTION Because of their acknowledged importance for barrier homeostasis, increasing attention has focused on stratum corneum lipids as potential topical therapeutic agents. Prior studies indicated that disruption of barrier function by either tape stripping or organic solvent treatment increases epidermal synthesis of the three major stratum corneum lipids, cholesterol, ceramides, and free fatty acids (1-3). Moreover, each of these three key lipids is required for barrier function, as demonstrated by the ability of pharmaco- 157