The extensive procedure required to measure percutaneous absorption versus transepidermal water loss (TEWL) enhances the desire to find a correlation between the 2 measurements to more easily assess skin barrier function. Experimentation investigating the correlation between TEWL and percutaneous absorption has yielded mixed findings. Yet despite the significant quantitative correlation demonstrated in some experiments, the precise qualitative relationship between percutaneous absorption and TEWL remains unsettled.
In the present article, we review some major studies defining the correlation between TEWL and percutaneous absorption and discuss major assumptions made in these experiments.
Oestmann et al investigated correlations between TEWL and hexyl nicotinate (HN) penetration parameters in humans. HN penetration was indirectly measured by means of Laser-Doppler Flowmetry (LDF), which quantifies the increase in cutaneous blood blow (CBF) caused by penetration of HN, a vasoactive substance. LDF parameters to and tmax were compared with corresponding TEWL values and a weak quantitative negative correlation was made (r = –0.31, r = –0.32). This correlation suggests that when an individual’s response time, to, was fast, the skin barrier was impaired.
Lamaud et al investigated whether permeability changes of hydrophilic compounds (TEWL) are correlated to those of lipophilic compounds (hydrocortisone). The results suggest TEWL can predict the changes of skin permeability to lipophilic drugs in normal and some damaged skin.
Lavrijsen et al characterized the stratum corneum (SC) barrier function in patients with various keratinization disorders using 2 noninvasive methods: measuring outward transport of water through skin by evaporimetry (TEWL) and the vascular response to HN penetration into the skin determined by LDF. This paper concludes that TEWL and HN penetration injunction are suitable methods to monitor skin barrier function in keratinization disorders and are helpful in discriminating between some of these disorders.