Microspectroscopic Confocal Raman and Macroscopic Biophysical Measurements in the in vivo Assessment of the Skin Barrier: Perspective for Dermatology and Cosmetic Sciences.

Skin barrier function, confined to the stratum corneum, is traditionally evaluated using established, noninvasive biophysical methods like transepidermal water loss, capacitance and conductance. However, these methods neither measure skin molecular composition nor its structure, hindering the actual causes of skin barrier change or impairment. At the same time, confocal Raman microspectroscopy (CRS) can directly measure skin molecular composition and structure and has proven itself to be a powerful technique for biomolecular analysis. The aims of this literature review were to evaluate noninvasive biophysical methods in view of CRS and to outline a direction towards more specific and informative skin measurement methods. We address this by investigating, for the first time, the relation between in vivo assessment of the skin barrier using indirect biophysical methods and the actual skin composition and structure as given by CRS, and emphasize the high potential of CRS for dermatology and cosmetic sciences. CRS acceptance in these fields will require close collaboration between dermatologists, skin scientists and spectroscopy experts towards simplifying the technology and creating robust, rapid, easy-to-use and less expensive CRS applications.