Supplementary Material for: Stratum corneum hydration measurements with a Bluetooth wireless probe: A real life study at home compared to measurements under laboratory conditions

Introduction and aims: Non-invasive measurement of the stratum corneum hydration (SCH) with capacitance-based instrumentation is established in dermatological and cosmetic studies. We wanted to test the reliability of non-invasive self-measurements for SCH performed under real-life conditions by volunteers with a Bluetooth-based (wireless) probe Corneometer® (CM825i) transmitting the data via a smartphone application to a central server. Probes and smartphones communicated using Bluetooth Low Energy (BLE). Data from the smartphone was securely transferred to a remote server in a different country with TLS encryption using HTTPS protocols. CM825i values were correlated with the established CM825 under laboratory conditions. The primary endpoint was the correlation of the two probes. Secondary endpoints were the coefficient of variation (CV) and delta values (before and after treatment). Material and methods: 18 healthy volunteers (f:8; m:10) participated in the prospective observational study. The real-world home use of the wireless CM825i was performed before and after treatments with base cream-DAC for 7 days. Results: Both instruments showed a significant and relevant correlation (p