CLEANSING BAR EVALUATION 325 is eliminated within a few hours (Figure 1) and limited to the upper horny layer (Figure 5). This means that the buffer capacity of the horny layer by far exceeds the amount of acid necessary to transform residues of surfactant-like soaps to fatty acids. These fatty acids are natural ingredients of skin surface (16, 17) and epidermal lipids (18). In contrast to this, the application of 100 p•l of 8% solution of soaps to a 1-cm 2 skin site under occlusive conditions causes a pH shift which lasts for more than 24 hours. There- fore, the applied quantity by far exceeds the buffer capacity of the treated horny layer. Under these circumstances the irritating molecular species are totally different from those which can possibly penetrate into skin during normal product use. Surfactants do not undergo such changes and their surface activity is rather independent of the pH value of the surrounding medium. Therefore, it must be concluded that a comparison of irritancy of soaps and surfactants via patch tests neglects the deactivation of soaps to fatty acids (likely to take place during normal product use) by overwhelming the buffer capacity of the skin's acid mantle. Normal unoccluded skin shows a pH shift from 5.5 to 6.8 after removal of 15 layers by stripping (19). Occlusion of skin for five days causes a steady increase of surface pH values from weakly acid to neutral values (20), probably due to equilibration of the horny layer with the interstitial fluid. Therefore, occlusion under Finn chambers will potentlate the adverse effects of a classical soap by shifting upward the skin surface pH. After application of the soaps, the skin surface remains depleted of pH-buffering sub- stances. There is no significant effect on the extracted tissue due to differences in pH values of 5-6 compared to 7-8. In both cases the buffer capacity of the skin surface is lowered and has to be restored during the following hours. This point of view is confirmed by the results of the investigation concerning the skin- care effect due to regular use of the soaps. The roughness of skin sites routinely treated with D is comparable to that treated with A and significantly smoother than that treated with B or C. Fissures which increase roughness values are one of the criteria which contribute to the scores describing the degree of skin damage after patch testing. Under the conditions of regular use, D and A apparently improve or do not worsen (Table VII) skin surface structure (21). The rate of water loss, which is another aspect of the structural integrity of the horny layer, was lower after treatment with classical soaps compared to treatment with A. An explanation may be found in Table VIII. Whereas skin treated with classical soaps deactivates soap anions (which certainly can enhance skin permeability (7) very quickly, surfactants remain unchanged and have to be eliminated by desquamation, permeation into deeper skin layers, microbial degradation, or mechanical wear-off. Generally, an- ionic surfactants including soaps are more irritating than water-insoluble lipids. Permeation of A is detectable up to at least eleven strips deep, while the traces of D disappear gradually after removal of six strips (Figure 6). The lowering of charge density of "untreated" sites after washing with water may be caused by removal of surfactants which might be the residues of preceding daily cleansing activities. The molecular identities of the fluorophors responsible for the phenomena described in Figure 4 are still unknown. Nevertheless, it is plausible that NADH contributes mainly to the signal excited at 360 nm and that it will be reduced in relation to the degree of inflammation (Table IV) (22 a/b).

326 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The potential of equal concentrations of D and of A to extract material of low molecular weight from the horny layer is different. One reason could be the much more pro- nounced ability of classical soaps to swell corneocytes (23) and skin. This more pro- nounced swelling would retard access of the solvent to cracks and fissures. Another reason might be the decreased adsorption of anionic surfactants to skin as the pH value of the medium rises (8,24). This phenomenon, which is more probably of a physico- chemical nature, will have influenced the extent of the adsorption of Rhodamine B (Figure 2). Higher losses of low molecular weight material strain the skin's natural buffering and waterholding capacity and could harm normal and damaged skin. Products have to be ranked according to functionality or efficacy (cleaning and skin care) and their skin compatibility or lack of irritancy. It can be recognized that a patch test is not an appropriate tool to compare classical soaps with surfactant-type soaps based upon the above-mentioned reasons. We recommend that consideration should be given to reevaluation of compatibility of soaps under conditions of environment, season, and regular use. Parameters more strongly related to in-use conditions are skin surface roughness, cleansing efficacy, extraction measurements, and the irritancy of the products under normal use. Apparently the seeming advantages of surfactant bar soaps may have been overestimated. The authors gratefully acknowledge the contribution of the Central Research Depart- ment of Beiersdorf (Dr. Meyer-Ingold) concerning the experiment including VERO- cells (22b). REFERENCES (1) P. J. Frosch and A.M. Kligman, The soap chamber test, a new method for assessing the irritancy of soaps, J. Amer. Acad. Dermatology, 1, 35 (1979). (2) J. M. Philip, "Anionic Surfactants Dermatological Observations (Human)," in Chr. Gloxhuber, An- ionic Surfactants, Biochemistry, Toxicology, Dermatology (Marcel Dekker Inc. Basel 1980), pp. 309-326. (3) W. Schneider, Alkalineutralisation und Hauttyp, Arch. f. Dermatology, 219, 620 (1964). (4) U. Hoppe, H.-J. Kopplow, and G. Sauermann, EinfluB von Puffersystemen auf die pH-Werte der Erwachsenenhaut, •rztl. Kosm., 7, 75-81 (1977). (5) H. Schaefer, A., Zesch, and G. Stiittgen, Skin Permeability (Springer-Verlag, 1982), pp S739-740. (6a) F. R. Bettley, The irritant effect of soap in relation to epidermal permeability, Br. J. Dermatol., 75, 113-116 (1963). (6b) F. R. Bettley, The influence of detergents and surfactants on epidermal permeability, Br. J. Der- matol., 77, 98-100 (1965). F. R. Bettley, The influence of soap on the permeability of the epidermis, Br. J. Dermatol., 73, 448-454 (1961). G. Sauermann, unpublished results. V. Blazek and V. Wienert, Der EinfluB der Hornschichthydratation auf den zeitlichen Ablauf des akuten UV-Lichtschadens, Strahlentherapie, 157, 280-286 (1981). M. R. Eftink and C. A. Ghiron, Fluorescence quenching studies with proteins, Analytical Blochem, 114, 199-227, (1981). (1 la) E. Burstein et M., Fluorescence and the location of tryptophan residues in protein molecules, Photo- chem. and Photobiol. 18, 263-279 (1973). (1 lb) G. B. Strambini and E. Gabellieri, Intrinsic phosphorescence from proteins in the solid state, Photo- chem. and Photobio/., 39, 725-729, (1984). 12) G. Schwedt, Fl•orimetrische Analyse (Verlag Chemie, Weinheim, FRG, 1981), p 42. 13) U. Hoppe, Topologie der Hautoberfliiche, J. Soc. Cosmet. Chem., 30, 213-239 (1979) "Stratum Corneum--Struktur und Funktion," in Cosmetic Technology, F. Klaschka, Ed. (Grosse-Verlag, Berlin, 1981), pp 141-158. 14) H. Bandmann and S. Fregert, Epicutantestung (Springer Verlag, Berlin, 1973). 15a) L-O. Lamke, G. E. Nilsson, and H. L. Reithner, Insensible perspiration from the skin under stan- dardized environmental conditions, Scand. J. Clin. Lab. Invest., 37, 325-331 (1977). (7) (8) (9) (10)