Biophysical measurements of human forearm, skin in vivo: effects of site, gender, chirality and time

Background/aims: Measurements of transepidermal water loss (TEWL) and skin colour are biophysical techniques commonly used to measure the in vivo skin effects of cosmetics, topical medicaments and chemical irritants. The purp ose of this study was to investigate the variability of TEWL and skin colou r on human forearm skin as a function of regional variation, gender and pre ferred chirality over an 8 h period. Methods: Biophysical measurements of TEWL and skin colour were made at five sites on both forearms of male (n=8) and female (n=9) human volunteers in vivo (38% relative humidity, 21 degrees C). Results: Rates of TEWL at the forearm midpoint were 10% lower than at the f orearm extremities (P<0.01). Skin redness (a*) near the wrist was 5-10% hig her than at other sites (P<0.05). Rates of TEWL were 5% higher in male volu nteers (P<0.05). Red and blue (b*) colour measurements of male forearm skin differed by 18% and 20% in comparison with female, respectively. Rates of TEWL, skin brightness (L*) and b* decreased by 9% (P<0.05), 1.8% (P<0.05) a nd 4% (P<0.05), respectively, with time whereas a* and skin temperature inc reased by 4.5% (P<0.01) and 7.2% (P<0.01), respectively. There was a signif icant correlation between the change in all measured parameters with time. Conclusions: Significant differences in TEWL and skin colour were identifie d that may have relevance in the design and interpretation of multivariate analyses of human forearm skin. Diurnal variation of TEWL, skin colour and temperature may have a single underlying mechanism.