Non-invasive assessment of stratum corneum structure and function.
Synopsis Methods for the study of the stratum corneum in situ are described and their application to clinical problems and cosmetic science are discussed. In vivo measurements of the thickness of skin and the components of skin can be made using high frequency pulsed ultrasound. Improved resolution of the device should allow measurement of epidermal thickness, and even that of the stratum corneum, which may vary with hydration. The protective ability of the stratum corneum can be estimated in a number of ways, the most familiar technique being transepidermal water loss measurements. Mechanical properties of the stratum corneum have been widely investigated in vivo by numerous researchers. A recent technique devised by us to deform the stratum corneum using an extendable metal frame has been used on patients with ichthyotic disorders. The deformation or compliance of the skin surface has been measured using profilometric methods, and compared to normal individuals. The results appear to be in agreement with the loss of flexural ability experienced by ichthyotic patients. Other mechanical methods more usually involve the measurement of the forces generated by skin while undergoing extension. Three techniques are described which have been used to investigate hydrational change with emollient application. Finally, the phenomenon of desquamation is discussed and methods presented for its evaluation. Passive collection of corneocytes using chambers is useful for estimation of the rates of desquamation, but are laborious and inconvenient. Forced desquamation using the desquamator enables rapid controlled harvesting of corneocytes. In addition to this, the dansyl chloride fluorescence technique has been adopted for estimation of stratum corneum kinetics using visual comparison and fluorimetric techniques. These techniques require further refinement and validation, but the tests available now are nonetheless important in understanding the biology and pharmacology of the stratum corneum.
Marks
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Department of Medicine (Dermatology), University of Wales College of Medicine, Health Park, Cardiff CF4 4XN, UK.
Edwards
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Black
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