Dehydration often goes unnoticed, whether during a long run or a day at the desk where you havent been having many fluids. The lack of fluid intake can impair both physical performance and cognitive focus. Recent advances in wearable technology aim to fill this gap by tapping into sweat as an accessible biofluid rich in physiological signals.
Researchers at UC Berkeley have repurposed electrodermal activity (EDA); which is usually used to gauge mental stress, to monitor hydration. Their SkinG sensor combines water‑permeable electrodes with a microfluidic channel in a thin, breathable patch that can be integrated into the back of a watch or fitness band. Seung-Rok Kim, a postdoctoral researcher in the Department of Electrical Engineering and Computer Sciences and co-lead author of the study,
“Because our sensor is thin, breathable and comfortable to wear, it can be seamlessly integrated into the back of a watch or fitness tracker to provide real-time feedback without bulky equipment or disposable components, this makes it easier for individuals to continuously track their physical exertion, hydration status and emotional stress throughout the day.”
Unlike non‑permeable electrodes that trap sweat and distort readings, the SkinG design allows fluid to pass through, maintaining stable skin contact and a reliable conductance signal. The research was published in Nature Electronics and can be found below:
Kim, S.-R., Zhan, Y., Davis, N., Bellamkonda, S., Gillan, L., Hakola, E., Hiltunen, J., & Javey, A. (2025). Electrodermal activity as a proxy for sweat rate monitoring during physical and mental activities. Nature Electronics. https://doi.org/10.1038/s41928-025-01365-7
Ali Javey, principal investigator of the study and professor of electrical engineering and computer sciences and of materials science and engineering said:
“This work opens the door to everyday, passive monitoring of hydration and stress using familiar wearable devices like smartwatches,”
In controlled trials, participants wore the sensor at multiple sites; wrist, forearm, upper arm and fingertip, while performing physical tasks such as cycling and mental tasks like IQ tests. The researchers found that skin conductance tracked sweat loss in real time: integrating the conductance signal over an exercise session accurately estimated total sweat volume and thus hydration status. Moreover, by comparing signals from different body locations, the system can distinguish between changes due to physical exertion and those driven by mental stress.
Graduate researcher Yifei Zhan and co-lead authors added that athletes could use these insights to time rehydration breaks optimally, while office workers might track stress levels to maintain productivity. He said:
“By making physiological sensing more accessible and personalized, this technology empowers people to make better decisions about exercise, rest and mental well-being,”
With sweat emerging as a practical route to health monitoring, devices like SkinG could soon join heart‑rate and step counters in smartwatches, offering users actionable feedback on hydration alongside physical and mental well‑being.
The project was conceived and led by Ali Javey (Departments of Electrical Engineering & Computer Sciences and Materials Science & Engineering, UC Berkeley) with equal contributions from Seung‑Rok Kim, Yifei Zhan and Noelle Davis, and experimental support from Suhrith Bellamkonda. Fabrication of the microfluidic electrodes benefited from the expertise of Liam Gillan, Elina Hakola and Jussi Hiltunen at VTT Technical Research Centre of Finland Ltd (Espoo and Oulu). The work was carried out in UC Berkeley’s Berkeley Sensor & Actuator Center and the Materials Sciences Division at Lawrence Berkeley National Laboratory, with partial support from Samsung Electronics Company, Ltd, the Bakar Fellowship and U.S. Department of Energy’s Electronic Materials (E‑MAT) program. Technical assistance from H. Sääskilahti and J. Rekilä was also gratefully acknowledged
Hassan graduated with a Master’s degree in Chemical Engineering from the University of Chester (UK). He currently works as a design engineering consultant for one of the largest engineering firms in the world along with being an associate member of the Institute of Chemical Engineers (IChemE).
