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 purpose of this study was to investigate the variability of TEWL and skin colour on human forearm skin as a function of regional variation, gender and preferred 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°C). Results: Rates of TEWL at the forearm midpoint were 10% lower than at the forearm extremities ( P <0.01). Skin redness ( a *) near the wrist was 5–10% higher than at other sites ( P <0.05). Rates of TEWL were 5% higher in male volunteers ( 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) and 4% ( P <0.05), respectively, with time whereas a * and skin temperature increased by 4.5% ( P <0.01) and 7.2% ( P <0.01), respectively. There was a significant correlation between the change in all measured parameters with time. Conclusions: Significant differences in TEWL and skin colour were identified 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.