It has been speculated that dry skin results from dysfunction of epidermal permeability barrier. But so far, there is no sufficient evidence to support this speculation. In fact, dry skin indicates low levels of stratum corneum hydration. Stratum corneum hydration levels are primarily determined by the content of natural moisturizers in the skin, while epidermal permeability barrier is mainly regulated by intercellular lipids and structural proteins in the stratum corneum. If dry skin is due to a defective permeability barrier, stratum corneum hydration levels should be inversely correlated with transepidermal water loss (TEWL) , an indicator of epidermal permeability barrier function. But no negative correlation has been demonstrated between stratum corneum hydration levels and TEWL in either normal human skin, ichthyoses lesions of patients, or sebaceous gland-deficient mice in a number of studies. In contrast, a positive correlation between stratum corneum hydration levels and TEWL was observed in normal human skin. Taken together, a line of evidence suggests that dry skin unlikely indicates epidermal permeability barrier dysfunction.

Objective:To determine whether the transepidermal water loss rate (TEWL) is correlated with the stratum corneum (SC) hydration level.Methods:Healthy children aged ≤ 17 years were enrolled from Medical Center for Public Health of Puning, 2 kindergartens and 2 primary schools, from October 2021 to June 2022. TEWL and SC hydration levels were measured on the left forearm and right anterior shank using a device for measuring skin physiological funcitons. Pearson correlation analysis was used to determine the correlations between TEWL and SC hydration levels in children of different ages and genders.Results:A total of 1 396 healthy children were enrolled, aged from 1 month to 17 years. Among them, 783 were male children and 613 were female children. In children aged 1 to < 12 months, no correlation was observed between TEWL and SC hydration levels on the forearms of male children, while TEWL was positively correlated with SC hydration levels on the anterior shanks of male children, as well as on the forearm and anterior shanks of female children ( r = 0.283, 0.404, 0.420, respectively, all P < 0.05) . In children aged 1 to 2 years, positive correlations were observed between the above two indicators on the anterior shanks of male children and forearms of female children ( r = 0.370, 0.419, respectively, both P < 0.01) , while there were no correlations between the two indicators on the anterior shanks of female children or forearms of male children. Positive correlations were observed between TEWL and SC hydration levels on both the forearms and anterior shanks of female children and the forearms of male children aged 3 to 5 years and 6 to 11 years ( r values ranging from 0.172 to 0.293, all P < 0.05) , but not on the anterior shanks of male children aged from 6 to 11 years. The group aged 12 to 17 years exhibited significantly positive correlations between TEWL and SC hydration levels on both the anterior shanks and forearms of male and female children ( r values ranging from 0.269 to 0.485, all P < 0.001) . Conclusion:SC hydration levels are positively correlated with TEWL on the anterior shanks and forearms of healthy children, and the degree of correlation tends to increase with age.