Influence of the time of occlusion on the quantitative parameters obtained by modelling trans-epidermal water loss curves to describe the human cutaneous barrier function in vivo.

Understanding the human cutaneous barrier function is one of the main goals in the study of skin physiology. The plastic occlusion stress test (POST) is a well-known, dynamic approach for studying the barrier, evoking an over-stimulation of the cutaneous water assessed by the trans-epidermal water loss (TEWL) measurement. Rigorous data analysis is imperative, and the compartmental model proposed is particularly suitable for this purpose. It provides a dynamic quantitative description of water mass, but also helps to disclose the relative influence of other factors, such as the time of occlusion. Ten healthy volunteers were submitted to POST studies with different occlusion periods (1 h, 6 h, 12 h and 24 h), allowing the full application of the model to the measured desorption curves. After fitting, the influence of the occlusion time over the evaporation half-lives (t1/2evap) is apparent (t1/2evap ranging from 2.46 min for 1 h of occlusion to 8.53 min for 24 h), increasing with time. Considering the wide applicability of the POST to the study of in vivo cutaneous physiology and pathophysiology, these results demonstrate that the time of occlusion must be considered as a key factor in POST measurements.