162 JOURNAL OF COSMETIC SCIENCE 135 130 '• 125 i • 120 - __. a= T ..... 105 100 95 90 [] Laceran Spezial Creme ß Laceran Spezial Creme 5% Urea ..: E F G H I volunteer 4OO 300 200 A B C D E F G H b volunteer J K L [] Laceran Spezial Creme ß Laceran Spezial Creme 5% Urea J K L Figure 5. Comparison of Laceran © Spezial Creme and Laceran © Spezial Creme 5 % Urea in relation to their hydration (Figure 5a) and the increasing urea content of stratum corneum (Figure 5b). Means and standard deviations of the estimation of skin hydration were calculated from six measurements at each test site. The corneometer units of the test site after the treatment were related to the value before treatment (tO) and the corneometer units of the control site. to a reduced concentration gradient of urea between stratum corneum and wash solution. Only a limited compensation of urea loss during the washing procedure can be achieved with urea supplementation of cleansing products. On the other hand, a considerable supply of urea to stratum corneum can be achieved with urea-containing skin care formulations. For example, a prolonged treatment of skin with Laceran © Spezial Creme

UREA ANALYSIS OF STRATUM CORNEUM 163 5% Urea increases significantly the urea content of stratum corneum compared to an untreated area and a treatment with Laceran © Spezial Creme, respectively. The increased urea amount remains at a high level for at least 24 hours after final application. This lasting effect is a possible factor in the increased hydration of skin surface following treatment with the urea-containing product compared with the non-urea-containing control product. We would propose that the reduced amount of urea in skin extracts of skin areas treated with Laceran © Spezial Creme is caused by reduced extractability of urea as a consequence of a visible residual lipid layer even after 24 hours following final application. This, however, is not found for the Laceran © Spezial Creme 5 % Urea, which differs in basis formulation from the Laceran © Spezial Creme. Clearly, urea treatment of skin causes an increase of skin hydration as measured by corneometry. This enhancement results in an improved clinical appearance, i.e., smooth- ness, scaliness, or erythema, of patients with dry or xerotic skin (5, 6, 16, 17). Our results support the concept of treatment of skin diseases, e.g., atopic dermatitis, or conditions of clinical dry skin with urea-containing products to compensate for the reduced amount of urea in stratum corneum (1). REFERENCES (1) W. Raab, Harnstoff in der Dermatologie, TIV Dermatol,, 23, 257-269 (1993). (2) W. Wohlrab, Zur Verwendung von Harnstoff in der Dermatologie, Dr. Derm., 36, 528-537 (1988). (3) H.W. Spier and C. Carrie, Hornschichtphysiologie als gewerbedermatologische Grundlagenfbrsch- ung, BerujS-Dermatosen, 15, 121-146 (1967). (4) G. Swanbeck and G. Rajka, Antipruritic effect of urea solutions, Acta Derm. Venereol. (Stockholm), 50, 225-227 (1970). (5) J. Serup, A double-blind comparison of two creams containing urea as the active ingredient, Acta Derm. Venereol. (Stockholm), Suppl. 177, 34-38 (1992). (6) J. Serup, A three-hour test for rapid comparison of effects of moisturizers and active constituents (urea), Acta Derm. Venereol. (Stockholm), Suppl, 177, 29-33 (1992). (7) H. W. Spier and G. Pascher, Die wasserli3slichen Bestandteile der peripheren Hornschicht (Hauto- berfiiiche), Arch. Dermatol. Syph., 199, 411-427 (1955). (8) O. Jacobi, Die Inhaltsstoffe des normalen Stratum corneum und Callus menschlicher Haut, Arch. Derm. Fo,xch., 240, 107-118 (1971). (9) L. Kerscher and J. Ziegenhorn, "Urea" in MethodJ of Enzymatic Analysis, 3rd ed., J. Bergmeyer and M. GraB1, Eds. (VCH-Verlagsgesellschaft mbH, Weinheim, 1985), Vol. 8, pp. 444-453. (10) E. Schwarz, Freie Aminosiiuren und verwandte Verbindungen in der abschabbaren Hornschicht un- befallener Haut von mikrobiellen Ekzematikern und Hautgesunden, Arch. Derre. Forsch., 242, 87-96 (1971). (11) E. Schwarz, Biochemische Stigmata menschlicher Hautoberfi•/che im Alter, Z. Klin. Chem. Klin. Blochim., 12, 93-97 (1974). (12) E. Schwarz, Neurodermitis und Hornschicht, Z. Hautk., 52 (Suppl. 2), 59-64 (1977). (13) G. Kloss and E. Schwarz, Freie Aminos•/uren und andere Ninhydrin-positive Substanzen in normalet Hornschicht und in Psoriasis-Schuppen, Arch. Klin. Exp. Dermatol., 228, 188-198 (1967). (14) J. Koyama, I. Horii, K. Kawasaki, Y. Nakayama, Y. Morikawa, and T. Mitsui, Free amino acids of stratum corneum as a biochemical marker to evaluate dry skin, J. Soc. Cosmet. Chem., 35, 183-195 (1984). (15) J. Ennen and D. Hiintschel, unpublished data (1997). (16) G. Swanbeck, Urea in the treatment of dry skin, Acta Derm. Venereol. (Stockholm), Suppl. 177, 7-8 (1992). (17) P.D. Pigatto, A. S. Bigardi, C. Cannistraci, and M. Picatrio, 10% urea cream (Laceran) for atopic dermatitis: A clinical and laboratory evaluation, J. Dermatol. Treat., 7, 171-145 (1996).