What sweat can tell you about your health

Scientists have devised a wearable sweat monitor that keeps tabs on your health by monitoring the chemical composition of your perspiration.

The new device, described Wednesday in Nature, is flexible enough to move with the body and has Bluetooth capabilities so it can send information in real time to a smartphone. 

Someday it could alert sweat drenched users to risks of dehydration, fatigue, stress and other physical ailments, making activity monitors like Fitbit look awfully basic.

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"The goal, ultimately is to have a pathology lab right on the body," said Ali Javey, a professor of electrical engineering at UC Berkeley and the senior author on the paper. 

For now, the group's monitor can track the levels of four biomarkers in sweat including electrolytes like sodium and potassium, and metabolites like glucose and lactate. It also has a sensitive temperature sensor.

The authors note that low levels of sodium and potassium in sweat could signal the onset of muscle cramps and dehydration, while monitoring glucose in sweat could provide clues to glucose levels in the body. Sweat lactate levels have been shown to be correlated with low blood flow in certain parts of the body. 

But this is only the beginning, Javey said. The team is already looking at an array of other proteins, molecules and ions that could offer more clues to a person's physical well being.

For decades, doctors have relied primarily on blood, and to a lesser extent urine and saliva, to get information about how well the body is functioning in a specific moment in time. Sweat was one bodily fluid largely missing from that panel, mostly because collecting enough perspiration to use in a chemical analysis was challenging.

The new monitor still requires the user to be perspiring, but they do not have to be dripping with sweat for the sensors to work. Javey explained that the sensors can get accurate measurements from just 1/10th of a droplet of perspiration. In the future, he'd like to see that amount get even smaller.

"The long term goal is to see if we can work with minimum amount of body liquid, so you won't need to exercise for the monitor to work," he said.  

The new device is not the first wearable sweat monitor, but it is one of the first to measure a suite of biomarkers at the same time. 

Javey said the group had two major challenges. First, they had to design four sensors that each track a single chemical in the complex chemical world of perspiration. Then, they had to make sure that those readings were interpreted correctly as environmental factors like temperature changed.

"A change in temperature can change the output of a sensor," he said. "When you start to sweat your temperature drops -- that's how the body dissipates heat. But as you keep exercising your temperature goes back up."

To ensure the readings are accurate over time, his group built a small, flexible computer that can calibrate the temperature reading with the sensing data. 

The sensors are plastic based and disposable, and rest on the skin. They attach to a flexible circuit board that can be reused. The entire system can be tucked into an athletic wristband or headband to make wearing it more comfortable.

Jason Heikenfeld, an electrical engineer at the University of Cincinnati, said the new sweat monitor looks impressive.

"Making a wearable band that electrochemically senses sweat analytes is extremely difficult," he wrote, in a News and Views article in Nature.

He notes that more work needs to be done before sweat monitors become commercially available but adds that the remaining challenges to not seem insurmountable.

In the future, he predicts, we may no longer remember how we lived without our personalized sweat trackers.

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