Transonychial water loss: relation to sex, age and nail-plate thickness.

The transonychial water loss (TOWL) was measured in 21 healthy volunteers with an evaporimeter, to establish the usefulness of this technique and study the influence of sex, age and nail-plate thickness. The median TOWL was 19.4 g/m2 h-1 and it decreased with increasing age (R = 0.51, P less than 0.018). The median transepidermal water loss (TEWLHAND) from the back of the hand was 16.0 g/m2 h-1 and from the dorsal side of the underarm (TEWLARM) it was 5.6 g/m2 h-1. The TEWLARM was significantly less than from any of the two other points studied (P less than 0.01), while there was no significant difference between the values obtained on the hand and the nail. TEWLARM had a median value of 6.4 g/m2 h-1 in men and 4.3 g/m2 h-1 in women (P less than 0.05) in this study. No significant correlation between nail-plate thickness, as measured by ultrasound 20 MHz A-scan, and TOWL was found. Measurements of TOWL are of interest and should be age-related. Further studies are needed to determine TOWL in various forms of nail pathology.