Most of us think of sweat as something gross that we don't want other people to notice, which is why antiperspirants and deodorants have become an $18 billion industry. But scientists are pretty interested in what comes out of your three million or so sweat glands, which can pump out as much as 1.6 quarts of fluid per hour when you're jogging on the treadmill.
Though about 99 percent of your perspiration is water, the chemical composition of the remaining one percent has the potential to reveal all sorts of critical information about your momentary physical state, such as whether you're becoming dehydrated or fatigued. Because the sweat glands excrete chemicals produced by your kidneys, lungs and other organs, your sweat can provide information about your overall health as well: think of it as personal big data.
And unlike blood or urine, sweat has a potentially big advantage. Since you perspire all the time, it's something that physicians and athletic trainers theoretically could monitor continuously, rather than having to stop and jab you with a needle or have you pee into a cup. The trick would be having a gadget that you could wear on your body to take tiny samples of your personal moisture — sort of Fitbit for sweating, and measure multiple chemical markers at once.
Wearable Perspiration Monitors
Well, as it turns out, researchers from the University of California Berkeley are already on the case. In an article recently published in Nature, they describe a new invention: A wearable, flexible plastic patch containing an array of electronic sensors that can detect glucose, lactate, sodium, potassium and body temperature. When sweat comes in contact with the sensors, the latter generate electrical signals, which are amplified and filtered by the device, and then calibrated using skin temperature. The data is then transmitted wirelessly to a smartphone app.
Here's a UC Berkeley video that shows how it all looks:
"Current commercially available wearable sensors are only capable of tracking an individual's physical activities and vital signs (e.g. heart rate)," says UC Berkeley professor of electrical engineering Ali Javey, principal investigator on the study, via email, "and fail to provide insight into the user's health state at molecular levels. To gain such insight, human sweat is an excellent candidate as it contains physiologically and metabolically rich information that can be retrieved conveniently and non-invasively."
The sensors are able to get accurate data from a tiny fraction of a single droplet of sweat. The electronic device is small enough to fit into a wristband or a headband. That's a big improvement over previous sweat-measuring technology, which required enough circuitry to fill a shoebox.
For athletes in endurance sports, this kind of wearable tech could be really useful for spotting drops in sodium and potassium that signal that dehydration and cramps are setting in. Measuring glucose could give an indication of how much of that chemical is present in an athlete's bloodstream to power his performance.
More Than Just Sports
But as Javey points out, this isn't just another training aid for professional athletes or fitness enthusiasts.
"They could also be used for a variety of physiological and clinical studies," he says. "The sweat biosensors could have multiple medical applications, including diagnosing a heavy metal poisoning, warning a person that they're in a severe enough depressive state to warrant medication and signaling that the body is getting an infection."
As Jason Heikenfeld, a University of Cincinnati engineering researcher explains in an accompanying Nature essay on the invention, future generations of wearable sweat-monitoring devices, might monitor even more chemicals. For example, the hormone cortisol, which is released when the body is in flight-or-fight mode, shows up in perspiration, so such a device could be a big help in managing stress, which increasingly is recognized as a major health problem in today's society.
And some medications and their metabolites — chemical byproducts created when the body breaks them down — also are excreted through the sweat glands. That might enable physicians to use sweat monitoring to keep tabs on the active amount of a drug in a patient's body, and to manage it to avoid ups and downs.
Javey says the researchers have filed a patent application for the sweat-monitoring technology, and he hopes to see it on the market in a few years. He'd also like to perfect it so that data can be obtained from even smaller amounts of perspiration. That would enable a person to wear the device and generate information throughout the day, even when he or she isn't exercising. The goal, as Javey has put it, is "ultimately to have a pathology lab right on the body."