REMOVAL OF STRATUM CORNEUM BY SCRUB CREAM 117 25 • 2o y- 0.83x r - 0.38 p 0.05 + 12.71 I • I I I • | ' " I | | : I I I 0 3 6 9 12 Number of tape strippings Figure 3. Cutaneous blood flow value, CBFV, after challenge with SLS as a function of number of tape strippings. The dotted line shows the result from the scrubbed area. Results are expressed as means of data obtained from nine individuals. The bars indicate S.D. enabled us to compare the effects of scrubbing with that of stripping. The skin reactions were visually ranked according to the degree of irritation and then objectively measured using TEWL and CBFV. The same order of rank was obtained with all three methods of evaluation. The visual ranking indicated that scrubbing corresponds to about three tape strippings. The objective assessments gave values between 1.4 and 2.9, depending on the calculation method used (see Results). The greatest difference was obtained for the CBFV assessment between the value read from the standard curve and that calculated from each individual. One reason for this difference is the difficulty in obtaining accu- rate CBFV readings when the skin reaction does not produce a homogeneous erythema. This is most likely to occur at weak skin reactions, due, for instance, to biological variations in skin response and vascular anatomy. In such cases, the linear regression analysis of the values from a single individual could give misleading results. In normal skin, fully differentiated corneocytes are continuously being desquamated from the surface. The use of a scrub cream accelerates this removal. From the obtained results, one can roughly estimate how many days in advance the outermost portion of the skin is lost by the use of a scrub cream. The daily production of stratum corneum

118 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 4. Three-dimensional computer visualization of replicas (6 X 3 mm) from human skin. a) Before treatment b) after washing and c) after scrubbing. For illustrative purposes the vertical scale has been magnified five times in relation to the horizontal.