Depth profiling of Stratum corneum hydration in vivo: a comparison between conductance and confocal Raman spectroscopic measurements

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    Different values for the measuring depth of the Corneometer have been reported in the literature. The manufacturer claims the value of 10–20 μm below the SC surface (7) and the European Group for Efficacy Measurements on Cosmetics and Other Topical Products (EEMCO) – 60–100 μm below the SC surface (19). A study with inserted isolating sheets between the probe and the SC surface has found that the measured signal drops to 50% of its original value after 12 μm (20).

Mila Boncheva, Corporate R&D Division, Firmenich SA, PO Box 239, Route des Jeunes 1, CH-1211 Geneva 8, Switzerland, Tel.: (41) 22 780 3027, Fax: (41) 22 780 3334, e-mail: mila.boncheva@firmenich.com

Abstract

Abstract:  The high-frequency electrical conductance of tape-stripped human skin in vivo can be used to evaluate the hydration profile of Stratum corneum (SC). Tape-stripping provides access to the underlying SC layers, and the conductance of these layers (as measured by the Skicon instrument) correlates well with their water content, as demonstrated by independent confocal Raman spectroscopic measurements. The correlation shows high inter-individual variance and is not linear over the full measurement range of the instrument, but is helpful to discriminate between dry, normal and highly hydrated SC. The depth profile of hydration in tape-stripped SC corresponds to the one in intact SC only if the barrier function of the skin is not impaired. Thus, conductometry of tape-stripped skin must be used in conjunction with a method that allows to estimate the barrier damage inflicted to SC during the tape-stripping procedure, for example, measurement of the trans-epidermal water loss. The methodology described here is simple, rapid and minimally invasive, and it employs commercially available instrumentation that is cheap, portable and easy to use. This approach is applicable to in vivo estimation of the SC hydration in studies in the areas of dermatology, skin care and transdermal drug delivery.

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