Digitizing Hydration: Tattoo-Like Sensor Could Save Lives

Even a 1-2 percent drop in body water can impair concentration, slow reaction times, and reduce endurance, which makes dehydration not only uncomfortable but also dangerous for athletes, industrial workers, and the elderly. Most of the time, this is due to the fact that the human brain isn’t great at telling us when we’re thirsty.

A team of researchers at the University of Texas in Austin, led by Nanshu Lu, professor at the Cockrell School of Engineering, has recently unveiled a new device that can measure your body’s hydration levels which could alert you when you might need a drink.

A new way to measure hydration 

Lu’s research spans engineering, material science, manufacturing, electronics, and biomedicine. She is primarily focused on bridging human and robotic sensing. Her laminated electronic tattoos monitor physiological signals providing continuous, uninterrupted monitoring of a person’s heart, brain, and muscle activity and have paved the way for soft robotic e-skins.

Similarly, this latest device also utilizes e-tattoo tech and solves a lot of the traditional challenges of testing a person’s hydration levels. Although the finished device looks straightforward, Lu notes that it took nearly seven years of trial and error—from formulating the hypothesis to testing hardware and signal processing, to securing clinical trials with patients on diuretic drugs before they could publish their results.   

Currently, the gold standard for testing is through a blood draw and osmolarity tests, which measure the concentration of water in the blood. This process is invasive and requires medical intervention. Urine tests are also an option. However, they are imprecise and vary widely from person to person. If you’re someone who simply wants to know how much water you need to drink, these options are not intuitive.

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To develop the device, Lu and her team first had to look at the role water plays in a person’s body. From regulating temperature to supporting gas exchange in the lungs to carrying essential nutrients throughout the body. 

“Our body is a soft ionic machine full of sodium, chloride, potassium, and calcium,” Lu said. “The more hydrated our body is, the more conductive it is.” 

The researchers theorized that this conductivity could be measured with external sensors through a process known as bioimpedance, a technique that measures how electrical signals pass through the body. 

The new hydration sensor works by sending a tiny alternating current across the upper arm and measuring how easily it passes through skin, muscle, and bone. Since the body is full of ions, water content directly affects electrical conductivity—when you’re hydrated, tissues conduct better; when you’re dehydrated, resistance increases. Unlike wrist- or skin-only sensors, this device places electrodes across the arm so the current flows through deeper tissues, making the reading more representative of total body water. 

“If the sensors are too close to each other, they only measure very local hydration, so we placed electrodes across the arm,” Lu explained. “We also chose a specific measurement frequency, 60 kilohertz, which flows through both intra- and intercellular fluids.”  

Her team also ran extensive computer simulations to model how currents would travel through the arm’s cylindrical structure, ensuring the design would capture whole-body hydration rather than just a superficial patch. 

Design for real-world use

The sensor is soft, wireless, and links to a smartphone via Bluetooth, allowing continuous tracking even during normal movement. In trials, its readings closely matched gold-standard whole-body impedance tests. 

“We found that if you have the right placement and the right frequency, the measurement is highly linear at a 0.99 correlation with whole body impedance,” Lu said. 

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The applications are wide-ranging: athletes who need to avoid dangerous heat stress, military personnel in extreme conditions, and patients in hospitals or nursing homes who cannot reliably communicate thirst. The next step in developing this device will be to test it in less controlled circumstances and to know how the device can be adapted to a wet surface, such as when a person sweats. In addition, the device’s durability needs to be tested to ensure it can withstand motion.

Lu’s work is a step toward a future where dehydration and its risks can be monitored invisibly, reliably, and in real time—helping improve quality of life for anyone who wears it. She envisions a future in which hydration sensing is only one layer of a suite of invisible e-tattoos, continuously monitoring heart, brain, and muscle activity to give doctors and individuals a complete digital picture of health. Her overarching goal is to develop tools to digitize the human body and revolutionize wearable technology. 

“Our current smartwatches will never measure my brain waves,” Lu said. “To truly care for our bodies, we need next-generation wearables that are not limited in placement or modality.” 

Cassandra Kelly is a technology writer in Columbus, Ohio.