New wearable sweat sensor can track your hydration status

Dehydration can sneak up on you. Whether you’re out jogging or sitting at a desk, it’s easy to lose track of your fluid intake. But a new, tiny sweat sensor may soon solve this problem. Designed by UC Berkeley researchers, this wearable device can measure changes in your hydration status and help you decide when it’s time to take a break and get some water.

In a study recently published in Nature Electronics, researchers demonstrated how their sweat sensor measures electrodermal activity (EDA), an electrical property of the skin, to monitor hydration levels during physical activity. Until now, EDA, or skin conductance, has been thought to be effective at assessing only mental stress.

These findings could broaden EDA’s role in physiological monitoring and someday provide a simple way for people to also avoid dehydration.

“This work opens the door to everyday, passive monitoring of hydration and stress using familiar wearable devices like smartwatches,” said Ali Javey, principal investigator of the study and professor of electrical engineering and computer sciences and of materials science and engineering.

According to Seung-Rok Kim, a postdoctoral researcher in the Department of Electrical Engineering and Computer Sciences and co-lead author of the study, the device’s innovative design is key to its efficacy and ease of use.

“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,” he said. “This makes it easier for individuals to continuously track their physical exertion, hydration status and emotional stress throughout the day.”

Co-lead author Yifei Zhan, a graduate researcher in the Department of Electrical Engineering and Computer Sciences, explained that athletes could use the device to avoid dehydration during training, while office workers or students might monitor stress to improve focus and balance. “By making physiological sensing more accessible and personalized, this technology empowers people to make better decisions about exercise, rest and mental well-being,” he said.

The scientific community had long questioned EDA’s usefulness in tracking physical activity, mainly because heavy sweating during exercise tends to saturate the skin and disrupt the signal, making it difficult for sensors to detect electrical changes to the skin. The researchers demonstrated how using breathable, water-permeable electrodes that prevent sweat from accumulating at the skin surface solves this problem.

The team designed and tested three types of water-permeable electrodes—micro-lace electrodes, spiral metal wire electrodes and carbon fiber fabric electrodes—to address a key limitation of conventional commercial electrodes, which are non-permeable and trap sweat under the sensor. After placing the electrodes on different parts of the body, they measured EDA as participants performed both physical tasks, like cycling, and mental tasks, like IQ tests.

“By comparing the EDA signals with localized sweat measurements and overall fluid loss from body weight, we evaluated how well each electrode tracked sweat production,” said Zhan. “This approach allowed us to identify effective sensor designs and body sites for using EDA to monitor hydration and to distinguish between signals caused by physical exertion and those driven by mental stress.”

According to the researchers, the study results show that skin conductance can reliably reflect sweat rate and hydration level across a range of physical and mental activities. Next, they will investigate how environmental conditions, like temperature, humidity and individual skin characteristics, affect the EDA signal.

“These efforts will help improve both the accuracy and personalization of next-generation wearable health monitors,” said Kim.