Methods for the Assessment of Barrier Function.

Due to the ease of skin accessibility, a large variety of invasive and noninvasive in vitro and in vivo methods have been developed to study barrier function. The measurement of the transepidermal water loss (TEWL) is most widely used in clinical studies. The different methods of determining TEWL, as well as skin hydration, skin pH, tape stripping and other modern less widely used methods to assess skin barrier function, are reviewed, including Raman spectroscopy and imaging methods such as optical coherence tomography and laser scanning microscopy. The modern imaging methods are important developments in the last decades which, however, determine the structure and, hence, cannot replace the measurement of TEWL in questions related to function.