The measurements took place at the right volar forearm, because this location is easy to access, mainly refrained from UV‐light damage, hair, and sebaceous glands, and often used as a standard anatomical site for skin barrier studies.3 , 22 , 23 , 24 All procedures were performed by one investigator (JGML). A circular area of approx. 3 × 3 cm was demarked with a pen at this location. The demarked skin was acclimatized to ambient air (room temperature: 22‐26°C; air humidity: 40%‐65%) for at least 10 minutes before start of measurements. Volunteers were placed in upright, sitting position during all study procedures.
First, SCH and TEWL were measured with the GPSkin once at the air‐exposed forearm. Then, SCH was determined by performing one measurement with the Epsilon. The Snapshot mode was used with a 5 seconds delay after first skin contact, and the average of three frames was calculated automatically. For both devices, moderate pressure was applied to keep contact with the skin surface. Thirdly, TEWL was measured with the Aquaflux. After calibration of this device, two measurements were performed with standard settings and a maximum measurement time of 180 seconds. The average of the two measurements was calculated. The Aquaflux was kept steady and perpendicular to the skin surface with very light skin pressure during measurements.
Next, the skin barrier of the demarked forearm location was disturbed using tapestripping, a noninvasive, painless, widely applied procedure to analyze SC barrier function without interfering with deeper, living epidermal keratinocytes.9 , 25 , 26 , 27 , 28 , 29 Repetitive adhesive tapes were applicated to the skin for 10 seconds with a standardized pressure pen (150 g/cm2; D'Squame) and sequentially removed until the skin became partly to homogeneously refulgent, corresponding to partial to almost complete removal of the SC; 13‐33 tapes per volunteer were needed. In this way, a wide range of SCH and TEWL values was obtained.
Directly after the tapestripping procedure, GPSkin, Epsilon, and Aquaflux measurements were repeated at the demarked location as described above. Lastly, one GPSkin measurement per cheek site was performed in each volunteer for later comparison to rosacea patients in pilot 2 (Figure1 ).
First, SCH and TEWL were measured with the GPSkin once at the air‐exposed forearm. Then, SCH was determined by performing one measurement with the Epsilon. The Snapshot mode was used with a 5 seconds delay after first skin contact, and the average of three frames was calculated automatically. For both devices, moderate pressure was applied to keep contact with the skin surface. Thirdly, TEWL was measured with the Aquaflux. After calibration of this device, two measurements were performed with standard settings and a maximum measurement time of 180 seconds. The average of the two measurements was calculated. The Aquaflux was kept steady and perpendicular to the skin surface with very light skin pressure during measurements.
Next, the skin barrier of the demarked forearm location was disturbed using tapestripping, a noninvasive, painless, widely applied procedure to analyze SC barrier function without interfering with deeper, living epidermal keratinocytes.
Directly after the tapestripping procedure, GPSkin, Epsilon, and Aquaflux measurements were repeated at the demarked location as described above. Lastly, one GPSkin measurement per cheek site was performed in each volunteer for later comparison to rosacea patients in pilot 2 (Figure
