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From firefighters to military personnel, from athletes to office workers, from babies to elderly people, undetected dehydration can threaten health in a variety of ways. Untreated diabetes, kidney disease, and medications that increase urination can result in dehydration. People usually aren’t aware of dehydration until they feel thirsty, at which point they are already dehydrated. The dangers of dehydration can include heat injury, heat exhaustion, urinary and kidney problems, seizures, cramping, and shock from low blood levels.

Scientists at North Carolina State University (NCSU) have developed a wearable hydration sensor that detects skin dehydration before it becomes a health issue. The device can be worn on the wrist or as a chest patch, and is lightweight, flexible and stretchable. In addition to the hydration sensor, the patch includes a strain sensor, three electrocardiography electrodes, a network analyzer chip, an ultra-low power microprocessor with Bluetooth, and a button cell battery. That hydration sensor is a capacitor with two parallel, silver nanowire electrodes in a matrix that works by measuring changes in impedance. Because the electrode is stretchable, it conforms to the skin. It’s not affected by external humidity and is pre-calibrated against a commercial skin hydration system. The end product can be used for other health measures, but the NC State focus is on continuous skin hydration monitoring.

According to NC State Ph.D. student Shanshan Yao, the lead author of a paper on the project, the sensor costs about $1 and a commercially manufactured version cost would be comparable to current wearables such as Fitbits. The data can be read on phones, tablets, or computers for application in the field, workplace, or clinical settings.