Epidermal and dermal hydration in relation to skin color parameters.

Background: Our goal was to investigate linkages between skin color parameters and skin hydration. Since most prior studies focused on stratum corneum hydration, we focused on epidermal and dermal hydration in relation to skin color parameters in both sexes.

Materials and methods: Thirty adults (16 female) with an age ± SD of 24.3 ± 0.6 years participated. Three sites on both volar forearms were evaluated for melanin index (MI), erythema index (EI), Individual Typology Angle (ITA), tissue dielectric constant (TDC) values to depths of 0.5 mm (TDC_0.5) and 2.5 mm (TDC_2.5), and Fitzpatrick skin type (FST).

Results: MI and EI were highly correlated (r = 0.800, p < 0.001) with maximum differences in MI and ITA along the arm of 3% and 6.3% with no difference between arms. Male MI was greater than females (p < 0.01). Male TDC_2.5 was 36.1 ± 5.4 and correlated with EI (r = 0.231, p = 0.035). Contrastingly, female TDC₂₅ was 28.5 ± 3.6 with no correlation with EI but was correlated with MI (r = -0.301, p = 0.003). These differential patterns held true for TDC_0.5. For both sexes, FST and ITA were highly correlated (r = -0.756, p < 0.001).

Conclusions: The findings revealed several correlations between skin color parameters and hydration that differed between males in females in some cases. The observed correlations may indicate that melanin may differentially impact water-holding capacity between sexes and provides a future research target. Further, these initial findings also may hold significance for dermatological assessments and the customization of skincare treatments tailored to individual skin types and demographics.