When you sweat during a workout, your body is trying to tell you something — and not just that you need a break.
Your perspiration is a fount of biomedical information. It reveals your body’s levels of water, electrolytes, and vital chemicals like glucose, cortisol, and lactate. Unlike a blood test, collecting sweat is painless, and it’s easier than serving up a urine sample.
“It turns out there’s a lot of information in a single drop of sweat,” said Roozbeh Ghaffari, chief executive and cofounder of Epicore Biosystems, a Cambridge company backed by $10 million in funding from investors that include Chevron Technology Ventures and Alumni Ventures.
Epicore’s first product, a skin patch to collect and analyze sweat, came to market last year in cooperation with PepsiCo, maker of the popular sports drink Gatorade. But another local company, Boston-based Nix Biosensors, will soon launch a rival product.
Nix, a 2016 spinoff from Harvard University’s Innovation Labs, has raised $7.5 million from investors including Techstars Boston and Stadia Ventures. The company has rung up 15,000 preorders of its $99 Hydration Biosensor, which is set to ship later this fall. The system includes an adhesive patch that constantly monitors sweat, along with a removable electronic pod that transmits the data to the user’s smartphone or smartwatch.
Each patch measures the rate at which users are losing water and electrolytes. It notifies users when they should take a drink and rehydrate. And it measures the overall composition of the sweat, to help athletes determine the right sports drinks for their individual needs.
”It makes a huge difference,” said Nix founder Meridith Cass, a nine-time marathon runner. “The No. 1 impact on your performance is going to be hydration.”
The starter kit comes with four single-use patches; additional patches cost $25 for a set of four. That makes the sensor a little pricey for casual athletes. Cass said that some of the product’s beta testers, including competitive triathletes and cyclists, use a fresh patch for each workout. But when training for a marathon, Cass settles for tracking her sweat output once a week.
By contrast, the Epicore Gx Sweat Patch costs $25 for a pack of two, twice as much as the Nix patches. But with Gx, users don’t attach an electronic device to read the results. Instead, they use a smartphone app — iPhone-only, for now — to scan the patch after each workout.
Epicore relies on technology developed at Northwestern University, where Ghaffari is an associate professor. Clear plastic tubes on the front of the patch show how much the user has sweated, while a set of colored bands indicates the amount of sodium in the sweat. The Gx app transmits a photo of the patch to a cloud-based server, which analyzes the image. In seconds, the phone shows the amounts of water and sodium the user has sweated out, along with recommendations on the best way to rehydrate (preferably with Gatorade).
People who do hard physical labor might also benefit from sweat testing. So Epicore has created a system that Ghaffari calls “a Fitbit for biochemistry.” It’s a reusable $100 device that attaches to a worker’s skin using a plastic patch that must be replaced after each use, at a cost of about $3. The system, called Connected Hydration, monitors water loss and electrolyte levels. The system can send alerts to a worker’s phone, warning him to boost his water intake. Chevron is helping to test it by issuing the devices to people working on offshore oil rigs.
But there’s a lot more in human sweat than water and salt.
“Sweat has a lot of the same biomarkers you find in your blood,” said Sameer Sonkusale, a professor of electrical and computer engineering at Tufts University who’s studied sweat-testing technology. “You can use it as a surrogate for continuous blood testing.”
Both Epicore and Nix are creating systems that can track these other substances. For instance, Nix is working on a patch to detect a person’s level of vitamin D, which is vital to bone development.
“Right now you have to go get a blood draw from a doctor to know if you’re vitamin D-deficient,” Cass said. “What if you can get that data continuously, at home and in real-time?”
Meanwhile, Epicore is developing a version that will pick up the user’s levels of lactate, an indicator of muscle fatigue, and cortisol, a hormone that’s associated with pain.
None of these products will work unless the user is sweating, but that doesn’t mean taking up long-distance running. Ghaffari said that a warm shower will do the job, by heating up the body just enough to produce a tiny amount of perspiration.