310 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS volumes per test site (50-100 I,tl/cm 2) (1). Application of soap solutions of such a high concentration and large volume per skin area over extended periods of time and under aggravating occlusive conditions causes inflammation which is not relevant to condi- tions of normal regular use (2). Procedures of the kind described (1) provoke adverse reactions and thus enable differen- tiation of products according to their irritancy. These findings are, strictly speaking, a result of the experimental conditions used. This aspect, viz., the influence of test con- ditions on test results, is especially important when classical or sodium-sterate/palmi- tate soaps are to be compared with surfactant-type cleansing bars. The potential of classical soaps to act as surfactants is limited to alkaline pH values within the sur- rounding medium. The surface activity of normal surfactants is, however, pH-indepen- dent over a wide range of pH values. Washing the skin with soap causes a temporary shift of the pH value to higher levels (3). This shift is reversed within two hours after washing by ingredients of the buffering system of the skin (4). In this weakly acidic pH range, the soap anions are transformed to uncharged fatty acids which are natural ingre- dients in skin lipids. In the case of surfactants, the skin-invading molecular species will not change their chemical configuration whether they are applied under a Finn chamber of under normal use conditions. In contrast, soaps will form two distinct kinds of molecules which act in a completely different way, as described above (5). In other words, in the case of surfactants the mode of application (Finn chamber test or regular use) will primarily cause only quantitative differences. In the case of soaps, however, there will be qualitative as well as quantitative differences. Surfactants and soaps usually increase the permeability of skin (6) as does the mainte- nance of both alkaline and strongly acid pH values at the skin surface (7). Tl•erefore the assumption seems quite logical that the irritation potential of soap solutions, applied in excess to the skin surface, is mainly caused by their alkaline pH value and the ability of soaps to act as surfactants at these alkaline pH values. The conclusion is that only the enormous excess of sodium palmitate/stearate solution, which temporarily exhausts the buffer capacity of skin, causes the more serious damage reported earlier, i.e., in Finn chamber tests, in comparison to the surfactant-type soaps. This could be verified by evaluating the irritation potential of the free fatty acids which form the soap. In order to investigate the differences between surfactants and soaps described above, we chose the following test procedures. Adsorption of cationic, fluorescent dyes can be used to measure the density of negatively charged groups at the skin surface, which may be due to two main groups of materials: a) Proteins and carbohydrates. b) Adsorbed surfactants which carry either a permanent (within the skin surface pH range which is of practical interest) or pH-dependant charge (8). Naturally skin contains many intrinsic fluorophors whose optical behavior depends on their molecular environment such as its polarity and concentration of quenchers (9). With excitation under constant conditions, the intensity and wavelength of skin's emission changes in relation to the degree of inflammation. Two ranges of fluorescence were selected: a) The range of fluorescence of tryptophan and possibly other related molecules at least protein-bound tryptophan is very sensitive to fluorescence quenching by oxygen

CLEANSING BAR EVALUATION 311 (10), fluorescence enhancement by humidity (11), and phosphorescence quenching (of tryptophan) (11) by humidity. b) The range of fluorescence of NADH (12). The concentration of NADH is decreased by inflammatory processes. The cleansing efficacy of products may be evaluated by fluorometric analysis of the residues of (extrinsic) skin-contaminating fluorophors after cleansing (8). The skin-care potential of products may be estimated by taking into account several parameters characterizing the structure of the horny layer: a) Skin profile measurements demonstrate objectively the evenness of the horny layer (13). The visual inspection of skin sites after patch testing includes the evaluation of fissures (14). b) Trans-epidermal water loss reflects the structural integrity of the horny layer (15). EXPERIMENTAL MATERIALS The following commercially available soaps were used as 2% and 8% solutions in dis- tilled water: A (surfactant-type soap, containing sodium-cocyl-isethionate-tallowate and isethianote etc.) B (classical soap) C (classical soap, containing amines as neutralizing agents) D (classical soap, sodium salts of fatty acids + additional lipids) EPICUTANEOUS TEST Visualscoring andskin surfacepH values. Twenty volunteers (10 m, 10 f average age • = 33.2 years s = 12.3) took part in the study performed December 3-11, 1984. The volunteers had healthy normal skin. Informed consent was obtained. 100 ptl of the two solutions (40øC) of each product were transferred to filter paper discs (diameter = 11 ram) fitted to Finn chambers (diameter = 11 ram manufacturer, Epitest Ltd. Oy, Helsinki, Finland). The chambers were fixed by Scanpor (Norge- plaster, Oslo, Norway) to the volunteers' backs 4 cm to the left and right of the spine. The products were applied in a randomized manner. The different dilutions were ap- plied at contralateral sites. An empty (control) chamber was also fixed within each column. Twenty-four hours after application the chambers were removed. Twenty-four hours after chamber removal the irritation was evaluated using the following scale: 0 = no reaction. 0.5 = weak erythema. 1 -- strong erythema. 1.5 = strong erythema, blisters, fissures. Immediately after removal of the chambers, the pH values of the residual solutions at the skin surface were measured by means of a conventional pH electrode.