A few aspects of transonychial water loss (TOWL): Inter-individual, and intra-individual inter-finger, inter-hand and inter-day variabilities, and the influence of nail plate hydration, filing and varnish

The aim of the study was to measure transonychial water loss (TOWL) in order to identify the extent of inter-individual, intra-individual inter-finger, inter-hand, and inter-day variabilities, and the influence of nail wetting, filing and varnishing on TOWL, with a view to determine parameters for the measurement of TOWL and its possible applications. Fingernail and toenail TOWL was measured using the condenser-chamber AquaFlux (Biox) and a specially designed Nail Adaptor supplied by Biox. A wide range of TOWL values (28–75 g/m2 h for fingernails and 26–48 g/m2 h for toenails) were found, with significant inter-individual variability. Intra-individual variability was lower; however, in the same individual, inter-finger, inter-hand/foot and inter-day variabilities were found, as well as a strong correlation between nail plate thickness and TOWL. Wetting the nails, even briefly, resulted in a significant rise in TOWL, which subsequently took much longer to return to control values. Filing the nail plate surface with a pharmaceutical file caused large increases in TOWL, whose profile (with number of filing strokes) was fairly different among individuals. As expected, nail varnish application reduced TOWL; the different extent of TOWL reduction by different varnishes suggests a potential use of TOWL measurements for product comparisons.