Potential Influence of Skin Hydration and Transepidermal Water Loss on the Dermal Transfer and Loading of Elemental Metallic Lead

The factors influencing transfer of chemicals or other contaminants to and from the surface of the skin are often poorly understood. Previous research has indicated that environmental conditions, skin hydration, and repeated contacts may all influence the quantity of dermal transfer. The aim of this analysis was to evaluate the influence of skin hydration and condition on quantitative chemical transfer in a series of systematic measurements using human subjects for 5 and 10 repeated contacts. Elemental metallic lead was used as the exemplar test substance for the measurements collected. Skin hydration index (HI) was assessed using a corneometer and skin condition and barrier function were measured using an open-chamber transepidermal water loss (TEWL) instrument. Results indicated that for the palmar surface of the index finger where sampling was conducted, the relative hydration level of the skin was higher for males (n = 6) versus females (n = 4) (mean HI = 4.0 for females; mean HI = 5.5 for males) but this difference was not statistically significant. Overall, the skin hydration level was not significantly associated with dermal loading for either the 5 contact scenario (Pearson correlation = 0.27; R-2 = 0.07; P = 0.45) or the 10 contact scenario (Pearson correlation = 0.26; R-2 = 0.07; P = 0.47). When the results were stratified by higher versus lower hydration levels (HI = 1-5 versus HI = 5-10), for the higher hydration levels (HI = 5-10; mean HI = 7), there was a moderately positive association between skin hydration and loading, but this was not statistically significant for either the 5 contact scenario (Pearson correlation = 0.75; R-2 = 0.56; P = 0.15) or the 10 contact scenario (Pearson correlation = 0.6; R-2 = 0.36; P = 0.28). No clear relationship was observed between the lower hydration levels (HI = 1-5) and dermal loading. For the palmar index finger, there was a negative correlation between the TEWL measurements and both the 5 contact (Pearson correlation = -0.45; R-2 = 0.2; P = 0.19) and 10 contact (Pearson correlation = -0.3; R-2 = 0.09; P = 0.4) scenarios, but this was not statistically significant. The results of this study are consistent with the limited results of other analyses, which have suggested that there may be nuances with respect to the effects of skin hydration on the quantitative dermal transfer to and from the skin, although additional data are needed to better understand these potential differences.