New Flexible Skin Patch Can Help Track Your Health Through Sweat

Just a drop of sweat can reveal a lot about a person’s body. Now, understanding some key components of your biochemistry can be as easy as slapping on an adhesive patch and swiping it near your smartphone. 

In a paper published this week in Proceedings of the National Academy of Sciences, a team of researchers announced the development of thin, flexible patches that can collect and analyze small quantities of sweat in real-time. 

“Soft microfluidic systems that capture, store, and perform biomarker analysis of microliter volumes of sweat, in situ, as it emerges from the surface of the skin, represent an emerging class of wearable technology with powerful capabilities that complement those of traditional biophysical sensing devices,” the paper’s authors write.

This patch uses color-changing chemistry to measure the wearer’s levels of glucose, lactate, chlorine, cortisol, and more. These can help assess various components of a person’s health, like their level of hydration and stress.  

“What we’re trying to do is to develop a suite of technologies that can be rendered in the form of a sticker,” co-author John Rogers, PhD, professor of biomedical engineering, materials science, and neurological surgery at Northwestern University, tells VeryWell. “This is kind of the high-water mark for us in terms of scope of functionality in a device of that type.”

How the Patch Works

Blood testing is the most common method of capturing information about certain key biochemicals like sodium, potassium, chloride, and urea. This process is invasive, however, as it requires pricking the skin or penetrating it with a syringe. This makes it less appealing as a routine process. 

Sweat, on the other hand, can be collected from the surface of the skin without any invasive actions. And it contains a number of biochemicals that are useful for understanding and shaping health outcomes.

Historically, collecting sweat was particularly challenging. It sometimes involved scraping it from the skin with a tool not unlike a squeegee. In grazing the skin, materials like skin cells, dirt, and oil could unintentionally pollute the sample. 

This new device uses microfluidic technology to direct small amounts of sweat through tiny channels, valves, and reservoirs in the patch. When sweat is released from pores in the skin, it travels through these pathways and interacts with assays—components to measure the composition of chemicals from the sweat. Not only does this stationary patch ensure the sweat sample is pristine, it also allows it to be analyzed in real-time. 

“These microfluidic platforms have changed the protocols you can use to study sweat,” Rogers, who is also the founding director of the Center on Bio-Integrated Electronics, says. 

The patches are relatively inconspicuous on the wearer. One reason for its small size and flexible structure is that the patch does not contain a bulky battery. Instead, it is powered through interactions with smartphones.

Harnessing near-range communication technology that enables functions like wireless payments, the patch and smartphone can effectively exchange power and information. The patch receives power wirelessly using radio waves from the phone, and information about the sweat—like how much was collected and its chemical make-up—is communicated back to the phone. 

The device must be in close proximity to a smartphone for it to operate, meaning the user has to swipe their phone close to the patch for it to receive power. But, Rogers says, scientists could develop a device with a larger antenna that could be installed on something like an exercise bike to get a more continuous read. 

What Sweat Can Tell Us

The non-invasive nature of sweat collection can be very useful, especially for people who rely on routine blood tests to measure their health status. 

“The disadvantage is that no one really knows all that much about sweat,” Rogers says. “It has these chemical components—that’s known. But how it stacks up against blood is an interesting research question and we’re right in the middle of that.”

His research group is working with a team of cardiologists at Lurie Children’s Hospital in Chicago to better understand how biomarkers in sweat compare to those in blood. For example, both sweat and blood contain glucose. The researchers will measure levels in both samples and assess if and how the two are correlated, in order to make the sweat sensors more accurate and useful. 

Measuring how cortisol, as well as glucose and vitamin C, are released in the body through sweat could also provide insight into the wearer’s mental health and physical stress. Cortisol is released in response to physical and mental stressors, and it can trigger glucose consumption when the body kicks into a fight-or-flight response. Additionally, increased cortisol levels are linked to conditions like obesity, diabetes, hypertension, and depression. 

The authors are hopeful that tracking these biochemicals through sweat will lead to a greater understanding of how cortisol, glucose, and vitamin C interact.

How Sweat-sensing Devices Will Be Used

Current smartwatch models—like the Apple Watch and the Fitbit—include tools to measure heart rate, movement, and blood-oxygen levels. To advance beyond these physical measurements, the addition of a sweat sensor would allow users to track biochemical properties and their impact on the user’s health as well. 

“I have a feeling that eventually, these big players in the market will take on sweat sensing because it’s not invasive,” Tolga Kaya, PhD, director of the engineering programs at Sacred Heart University in Connecticut, tells Verywell. “Once they implement it into their watches, then it’s going to go bigger.”

Based on research by Rogers and his team, Gatorade developed the GX Sweat Patch. The product is a simplified version of the one described in the study and only tests for factors relevant to athletes, like hydration and electrolyte levels. 

The product was announced via a commercial during half-time at the NBA All-Star game in February and will be available in sporting goods stores next year. The patch also crossed into the virtual realm as a product in the most recent version of the video game NBA 2K. 

This technology has various uses in the spheres of athletics and nutrition, including tracking sweat loss and electrolyte levels. 

 “You can tell if someone is hydrated or dehydrated in real-time, which is very helpful because when you notice that you are thirsty or dehydrated, it is already too late to bring it back,” Tolga says, who is not affiliated with the Northwestern paper. “You lose mental performance, physical performance pretty quickly.” 

Rogers and Tolga say these devices could also be useful for the military. To better maintain service people’s health, patches like these could assess their hydration and cortisol levels to ensure peak physical and mental performance.  

As scientists learn about how to engineer devices that coexist with living systems, there is room for incredible possibility. From implantable devices for the brain to patches to track neonatal health, Rogers says there are many ways new tools can help us better understand our basic biology. 

“It’s a really rich, broad space for doing discovery-oriented academic research,” Rogers says. “It’s sort of science with consequences, in a sense. If you develop an understanding, you might be able to create the foundations for technologies that could transform the ways we do health care with direct benefits and improved outcomes for the patients, reduced costs, and deployability in impoverished areas of the planet.”