Development and Performance Evaluation of a Capacitance-based Skin Moisture Meter

Asteatosis is characterized by excessive moisture loss from the stratum corneum, leading to skin dryness, itching, cracking, and susceptibility to bacterial infections and allergic conditions. While subjective clinical assessments remain the standard in the diagnosis of asteatosis, recent studies have aimed to objectively evaluate skin moisture through physicochemical measurements. However, the adoption of existing research instruments for assessing skin moisture in clinical practice is limited due to their high cost, bulky design, and inconsistent measurement results. This study addresses the issue of measurement variability by developing a capacitance-based skin moisture meter with an improved load stabilizing mechanism to stabilize the contact force between the sensor and the skin, which is a primary source of measurement error. The interaction at the sensor-skin boundary area is modeled using an equivalent electrical circuit, and the optimal measurement frequency is determined to enhance accuracy and reproducibility. Based on these findings, we developed a compact capacitance-based skin moisture meter capable of measuring water content as electrostatic capacitance with low variability. Performance of the instrument was evaluated using pig skin, chosen for its physiological similarity to human skin, by calculating the correlation between capacitance readings and gravimetric water content. In addition, to assess the measurement variability, water sorption and desorption tests were conducted using filter paper and water. The water content measured by the device showed a strong linear correlation with pig dermis water content (r = 0.9296) and an inverse correlation with total water loss across whole pig skin (r = −0.9066). In water sorption and desorption tests with filter paper, the mean coefficients of variation were 1.0% and 1.9%, respectively, indicating measurement stability comparable to or higher than that of existing research instruments. Although the aforementioned investigations were limited to pig skin and filter paper, these results suggest that the novel device possesses the essential performance required for accurate, low-variability measurement of human skin moisture.