Researchers are developing an innovative new way to track health and fitness. A skin patch has been developed that can test droplets of sweat to track health while people exercise. Testing showed that the patches would work even on sweaty bicyclists throughout a long-distance race in Arizona. Researchers revealed the details of the devices in a study published Wednesday in the journal Science Translational Medicine.

The sweat patch is slightly larger than a quarter and is made of flexible material that can bend and move with the body. The patch captures and analyzes tiny amounts of perspiration to measure things as hydration levels or electrolyte loss. Tiny channels on the patch route it to different compartments containing chemicals that react to composition of the sweat by changing colors. A smartphone app held over the patch takes a picture of the colors and interprets the information.

Human sweat contains many of the same biomarkers as blood and the results can be obtained more quickly than with a blood test. Lead researcher John A. Rogers, who directs Northwestern University’s Center for Bio-Integrated Electronics, said “Sweat has biochemical components within it that tell us a lot about physiological health.”

In the two studies detailed in the journal, 21 healthy volunteers had the patches stuck on their arms and backs to test how they performed. Twelve bicyclists wore the patches while competing in a long-distance outdoor race in Tucson while nine others rode exercise bikes in a gym and participated in a more conventional sweat test at the same time. The researchers found that the patches’ biochemical test results agreed with the indoor bikers’ conventional sweat test. The patches also worked in the challenging outdoor race, staying in place for the duration of the event.

The sweat patches are designed for one-time use over a few hours and is aimed primarily at athletes. They are clearly a step above today’s wearable technology that allows people to track their activity, heart rate, and calories with electronic sensors. In the future, Rogers envisions the technology being used to screen for diseases and monitor the effects of training regiments. A future design may be capable of multiple measurements over time.

The first-of-its-kind patch is part of an emerging field of wearable diagnostics. Other research groups around the country are also pursuing wearable biosensors. With additional research, more sophisticated use of such devices will be possible, providing consumers with tiny labs that can be stuck to their skin.

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