Transepidermal water loss (TEWL) and transonychial water loss (TOWL) measurements in healthy nail apparatus

Background: Although non-invasive diagnostic methods are widely used to examine the nail apparatus (NA), studies in healthy ones are scarce, and analyzes were often conducted in small groups. In the literature, there are only a few reports on TOWL measurements. The results of TEWL studies in the proximal nailfold have not been published so far. Materials and Methods: Based on a detailed interview and physical examination, 81 volunteers (40 women and 41 men) aged from 22 to 65 years were qualified for the study. In this study, the overall examination of the NA in relation to water loss was performed for the first time, regarding the hand (d, dominant; n, non-dominant) and finger types (number, start of count from thumbs) as well as sex and age. Results: The average TEWL value in the entire group ranged from 7.53 c.u. in the finger nd4 to 11.09 c.u. in nd1. Both in the dominant and non-dominant hand, in the entire analyzed group, and taking into account gender, weak statistically significant relationships were observed between the finger type value and TEWL (p < 0.05).The TEWL values were lower moving away from the thumb, The average TOWL value in the entire group ranged from 5.01 c.u. in d1 to 7.34 c.u. in d5. Both in the dominant and non-dominant hand, in the entire analyzed group and considering gender, statistically significant relationships were observed between the type of finger and TOWL values (p < 0.05). The TOWL values were higher moving away from the thumb. Subsequently, the values of TOWL and TEWL did not depend on type of hand (dominant or non-dominant), sex and age. Weak and moderate statistically significant correlations were found between TEWL and TOWL values in the entire study group and in females, as well as in selected fingers in males (d2, nd2, d3, nd3, d5, nd5) (p < 0.05, r < 0.27). Conclusion: Non-invasive diagnostics such TEWL and TOWL measurements are useful to assess differences in structure and function between types of fingers. However, obtained results demand further studies.