Someday, sweating might not just cool you down—it could also power your phone. So-called biobatteries, which can take the form of a temporary tattoo, can already generate a small amount of electricity, the Washington Post reports.

"We are working on enhancing (the product) so it can power small electronic devices," a researcher tells the BBC. The tattoos work using lactic acid that's found in our sweat.

But creating the devices wasn't researchers' original goal. Researchers were creating a new way to keep track of lactic acid, high levels of which can indicate a medical problem.

They placed a lactate sensor on temporary tattoo paper, making the tracking process easier. "I've worn it myself—you don't even feel it. It really is like a tattoo," says researcher Wenzhao Jia.

Then her team added an enzyme to the tattoo in order to extract electrons from the lactate, thus turning the device into a battery. (In other sweat-related technology, Kodak has been making anti-stink clothing.)

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