Three recent papers 1-3 described a new Instrument-GPkSin ® (GPOWER) represented in Figure 1-that records, in vivo, both the skin hydration status and the TEWL on the same skin site (a small skin area, ≈1 cm 2) within seconds, since integrating two probes within the same body. As this instrument is connected to a smartphone application via a Bluetooth system, the provided data are immediately transferred, together with date, time of the recording and environmental Temperature (C°). Not only the skin hydration status and TEWL values given by the GPSkin ® were found highly correlated to other validated instruments 4,5-Corneometer ® (Courage and Khazaka Company ™), Tewameter ® (Courage and Khazaka Company ™), Aquaflux AF200 ® (Biox systems ™)-but they were accurate enough to significantly differentiate two formulae containing slightly different and low Glycerol contents (eg, 7% and 10% w/w). In addition, as important finding, this instrument showed that the skin hydration provided by a formula with a very high glycerol content (40%), reduced the TEWL by about 50% on the same skin site. Although of an easy handling (ergonomic, light, etc), the GPSkin ® body has nevertheless to be gently applied perpendicularly onto the skin surface, a positioning needed by the TEWL probe to fully perform. Such verticality is less a limiting factor in the recording of the skin hydration as the two impedance-measuring electrodes (located in the skin-contacting crown) are always closely connected to the skin surface. These conditions were met in two previously quoted studies 1,3