The measurement of stratum corneum (SC) thickness from in-vivo Raman water concentration depth profiles is gaining in popularity and appeal due to the availability and ease of use of in-vivo confocal Raman measurement systems. The foundation of these measurements relies on high-quality confocal Raman spectroscopy of skin and the robust numerical analysis of water profiles, which allow for accurate determination of SC thickness. These measurements are useful for studying intrinsic skin hydration profiles at different body sites and for determining hydration properties of skin related to topically applied materials. While the use of high-quality in-vivo Raman instrumentation has become routine and its use for SC thickness measurement widely reported, there is lack of agreement as to the best method of computing SC thickness values from Raman water profiles. Several methods have been proposed and are currently in use for such computations, but none of these methods has been critically evaluated. The work reported in this paper describes a new method for the determination of stratum corneum thickness from in-vivo confocal Raman water profiles. The method represents a consensus approach to the problem, which was found necessary to apply in order to properly model and quantify the large diversity of water profile types encountered in typical in-vivo Raman water measurement. The methodology is evaluated for performance using three criteria: 1) frequency of minimum fitting error on modeling to a standard numerical function; 2) frequency of minimum model error for consensus vs. individual SC thickness values; and 3) correlation with reflectance confocal microscopy (RCM) values for SC thickness. The correlation study shows this approach to be a reasonable replacement for the more tedious and time-consuming RCM method with R 2 = 0.68 and RMS error = 3.7 microns over the three body sites tested (cheek, forearm and leg).
C. H. Watkinson, A. Moore and P. Coan, “Water Modulation of Stratum Corneum Chymotryptic Enzyme Activity and Desquamation,” Archives of Dermatological Research, Vol. 293, No. 9, 2001, pp. 470-476. doi:10.1007/s004030100257
L. Gerhardt, A. Lenz, N. Spencer, T. Münzer and S. Derler, “Skin-Textile Friction and Skin Elasticity in Young and Aged Persons,” Skin Research and Technology, Vol. 15, No. 3, 2009, pp. 288-298. doi:10.1111/j.1600-0846.2009.00363.x
Y. Tomita, M. Akiyama and H. Shimizu, “Stratum Corneum Hydration and Flexibility Are Useful Parameters to Indicate Clinical Severity of Congenital Ichthyosis,” Experimental Dermatology, Vol. 14, 2005, pp. 619-624. doi:10.1111/j.0906-6705.2005.00341.x
J. Sato, M. Yanai, T. Hirao and M. Denda, “Water Content and Thickness of the Stratum Corneum Contribute to Skin Surface Morphology,” Archives of Dermatological Research, Vol. 292, No. 8, 2000, pp. 412-417. doi:10.1007/s004030000143
M. Egawa and T. Kajikawa, “Changes in the Depth Profile of Water in the Stratum Corneum Treated with Water,” Skin Research and Technology, Vol. 15, 2009, pp. 242-249. doi:10.1111/j.1600-0846.2009.00362.x
I. Blank, J. Moloney, A. Emslie and I. Simon, “The Diffusion of Water across the Stratum Corenum as a Function of Its Water Content,” Journal of Investigative Dermatology, Vol. 82, 1984, pp. 188-194. doi:10.1111/1523-1747.ep12259835
J. Bouwstra, A. de Graaff, G. Gooris, J. Nijsse and J. Wiechers, “Water Distribution and Related Morphology in Human Stratum Corneum at Different Hydration Levels,” Journal of Investigative Dermatology, Vol. 120, 2003, pp. 750-758. doi:10.1046/j.1523-1747.2003.12128.x
K. Holbrook and G. Odland, “Regional Differences in the Thickness (Cell Layers) of the Human Stratum Corneum: An Ultrastructural Analysis,” Journal of Investigative Dermatology, Vol. 62, 1974, pp. 415-422. doi:10.1111/1523-1747.ep12701670
Y. Kalia, F. Pirot and R. Guy, “Homogeneous Transport in a Heterogeneous Membrane: Water Diffusion across Human Stratum Corneum in Vivo,” Biophysical Journal, Vol. 71, No. 5, 1996, pp. 2692-2700. doi:10.1016/S0006-3495(96)79460-2
F. Pirot, Y. Kalia, A. Stinchcomb, G. Keating, A. Bunge and R. Guy, “Characterization of the Permeability Barrier of Human Skin in Vivo,” Proceedings of the National Academy of Sciences of the USA, Vol. 94, No. 4, 1997, pp. 1562-1567. doi:10.1073/pnas.94.4.1562
J. Nikolovski, G. Stamatas, N. Kollias and B. Wiegand, “Barrier Function and Water-Holding and Transport Properties of Infant Stratum Corneum Are Different from Adult and Continue to Develop through the First Year of Life,” Journal of Investigative Dermatology, Vol. 128, 2008, pp. 1728-1736. doi:10.1038/sj.jid.5701239
K. Miyamoto, H. Takiwaki, G. Hillebrand and S. Arase, “Utilization of a High-Resolution Digital Imaging System for the Objective and Quantitative Assessment of Hyperpigmented Spots on the Face,” Skin Research and Technology, Vol. 8, 2002, pp. 73-77. doi:10.1034/j.1600-0846.2001.80202.x
J. Leyden and A. Rawlings, “Cosmetic Science and Technology Series Volume 25: Skin Moisturization,” Marcel Dekker, Inc., New York, 2002.
J. Rim, S. Jo, J. Park, B. Park and J. Y. Ji, “Electrical Measurement of Moisturizing Effect on Skin Hydration and Barrier Function in Psoriasis Patients,” Clinical Experimental Dermatology, Vol. 30, 2005, pp. 409-413. doi:10.1111/j.1365-2230.2005.01773.x
J. Nebus, F. Costes, W. Wallo and E. Kurtz, “Clinical Improvements in Skin Tone and Texture Using a Facial Moisturizer with a Combination of Total Soy and SPF30 UVA/UVB Protection,” Journal of the American Academy of Dermatology, Vol. 54, 2006.
P. Caspers, G. Lucassen and G. Puppels, “Combined in Vivo Confocal Raman Spectroscopy and Confocal Microscopy of Human Skin,” Biophysical Journal, Vol. 85, 2003, pp. 572-580. doi:10.1016/S0006-3495(03)74501-9
M. Egawa and H. Tagami, “Comparison of the Depth Profiles of Water and Water-Binding Substances in the Stratum Corneum Determined in Vivo by Raman Spectroscopy between the Cheek and Volar Forearm Skin: Effects of Age, Seasonal Changes and Artificial Forced Hydration,” British Journal of Dermatology, Vol. 158, 2008, pp. 251-260. doi:10.1111/j.1365-2133.2007.08311.x
M. Egawa, T. Hirao and M. Takahashi, “In-Vivo Estimation of Stratum Corneum Thickness from Water Concentration Profiles Obtained with Raman Spectroscopy,” Acta Dermato Venereologica, Vol. 87, No. 1, 2007, pp. 4-8. doi:10.2340/00015555-0183
J. Crowther, A. Sieg, P. Blenkiron, C. Marcott, P. Matts, J. Kaczvinsky and A. Rawlings, “Measuring the Effects of Topical Moisturizers on Changes in Stratum Corneum Thickness, Water Gradients and Hydration in Vivo,” British Journal of Dermatology, Vol. 59, 2008, pp. 567-577.
S. Bielfeldt, V. Schoder, U. Ely, A. van der Pol, J. de Sterke and K. Wilhelm, “Assessment of Human Stratum Corneum Thickness and Its Barrier Properties by in-Vivo Confocal Raman Spectroscopy,” IFSCC Magazine, Vol. 12, 2009, pp. 1-8.
J. Wu and T. Polefka, “Confocal Raman Microspectroscopy of Stratum Corneum: A Pre-Clinical Validation Study,” International Journal of Cosmetic Science, Vol. 30, 2008, pp. 47-56. doi:10.1111/j.1468-2494.2008.00428.x
M. Boncheva, J. de Sterke, P. Caspers and G. Puppels, “Depth Profiling of Stratum Corneum Hydration in Vivo: A Comparison between Conductance and Confocal Raman Spectroscopic Measurements,” Experimental Dermatology, Vol. 18, No. 10, 2009, pp. 870-876. doi:10.1111/j.1600-0625.2009.00868.x
H. Mogensen, H. Morsy, L. Thrane and G. Jemec, “Morphology and Epidermal Thickness of Normal Skin Imaged by Optical Coherence Tomography,” Clincal and Laboratory Studies, Vol. 217, No. 1, 2008, pp. 14-20.
J. Weissman, T. Hancewicz and P. Kaplan, “Optical Coherence Tomography of Skin for Measurement of Epidermal Thickness by Shapelet-Based Image Analysis,” Optics Express, Vol. 12, No. 23, 2004, pp. 5760-5769. doi:10.1364/OPEX.12.005760
S. Nouveau-Richard, M. Monot, P. Bastien and O. De Lacharriere, “In Vivo Epdiermal Thickness Measurement: Ultrasound vs Confocal Imaging,” Skin Research and Technology, Vol. 10, No. 2, 2004, pp. 136-140. doi:10.1111/j.1600-0846.2004.00067.x
T. Gambichler, R. Matip, G. Moussa, P. Altmeyer and K. Hoffmann, “In Vivo Data of Epidermal Thickness Evaluated by Optical Coherence Tomography: Effects of Age, Gender, Skin Type, and Anatomic Site,” Journal of Dermatological Science, Vol. 44, No. 3, 2006, pp. 145-152. doi:10.1016/j.jdermsci.2006.09.008
M. Mogensen, B. Nurnberg, J. Forman, J. Thomsen, L. Thrane and G. Jemec, “In Vivo Thickness Measurement of Basal Cell Carcinoma and Actinic Keratosis with Optical Coherence Tomography and 20-MHz Ultrasound,” British Journal of Dermatology, Vol. 1, 2009, pp. 1-7.
A. van der Pol, J. de Sterke and P. Caspers, “Modeling and Interpretation of Water Concentration Gradients in the Stratum Corneum as Measured by Confocal Raman Microspectroscopy,” Journal of Cosmetic Science, Vol. 29, No. 3, 2007, p. 235.
X. Yin, J. Goudriaan, E. A. Lantinga, J. Vos and H. J. Spiertz, “A Flexible Sigmoid Function of Determinate Growth,” Annals of Botany, Vol. 91, No. 3, 2003, pp. 361-371. doi:10.1093/aob/mcg029
J. A. Nelder and R. Mead, “A Simplex Method for Function Minimization,” Computer Journal, Vol. 7, No. 4, 1965, pp. 308-313. doi:10.1093/comjnl/7.4.308
M. Huzaira, F. Ruis, M. Rajadhyaksha, R. Anderson and S. González, “Topographic Variation in Normal Skin, as Viewed by in Vivo Reflectance Confocal Microscopy,” Journal of Investigative Dermatology, Vol. 116, 2001, pp. 846-852. doi:10.1046/j.0022-202x.2001.01337.x
P. Caspers, G. Lucassen, E. Carter, H. Bruining and G. Puppels, “In Vivo Confocal Raman Microspectroscopy of the Skin: Noninvasive Determination of Molecular Concentration Profiles,” Journal of Investigative Dermatology, Vol. 116, 2001, pp. 434-442. doi:10.1046/j.1523-1747.2001.01258.x
P. Caspers, G. Lucassen, H. Bruining and G. Puppels, “Automated Depth-Scanning Confocal Raman Microspectrometer for Rapid in Vivo Determination of Water Concentration Profiles in Human Skin,” Journal of Raman Spectroscopy, Vol. 31, No. 8-9, 2000, pp. 813-818. doi:10.1002/1097-4555(200008/09)31:8/9 3.0.CO;2-7