How skin hydration is measured
By Jeremy Fain, founder of Restelys. Updated 17 October 2026. 2 sources cited.
“Moisturises” should not be an impression. Dermatologists measure the water in the skin with precise instruments, and our claims will be held to them.
The upper layer of the skin conducts electricity better the more water it contains. Corneometers use this principle: a probe placed on the skin infers its hydration level, painlessly and in seconds.
European expert groups have defined protocols so that these measurements are reliable and comparable: temperature and humidity conditions, acclimatisation time for volunteers, repeated readings.
Before writing “moisturises” on the label of our body lotion, we will have its effect measured this way, on a panel of volunteers, at the durations we announce.
Sources
- Berardesca E. “EEMCO guidance for the assessment of stratum corneum hydration: electrical methods”. Skin Research and Technology, 1997.
- Fluhr J.W. et al. “Comparative study of five instruments measuring stratum corneum hydration”. Skin Research and Technology, 1999.