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You can learn a lot about health — and crime — through sweat

You can learn a lot about health — and crime — through sweat

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Sweating the small stuff — and the much larger, personally identifiable stuff

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ATP Masters Series: Monte Carlo Rolex Masters - Day Six
Rafael Nadal of Spain feeling the heat during his match against Dominic Thiem of Austria at the 2018 Rolex Monte-Carlo Masters in Monaco
Photo by Julian Finney / Getty Images

Most of the time, people want to sweat less. But the very liquid that we try so hard to avoid producing is a goldmine of data — and researchers want to harness it to do everything from combat stress to keep our phones more secure.

Sweat contains a mix of chemicals that not only tell us a lot about our current state, but is extremely distinctive to each of us. In other words, it can be a real giveaway, and there’s almost no chance of chance of any two people having the same sweat profile. In a paper recently published in the journal Analytical Chemistry, University at Albany forensic chemist Jan Halámek and his team analyzed 25 real samples of sweat taken from volunteers, and 50 fake sweat samples (which are basically artificial mixtures of the chemicals in sweat). By looking at the concentration of three chemicals (urea, glutamate, and lactate) in the sweat, they found that it was very simple to tell each of the sweat samples apart.

“Fingerprints remain the same and can be faked, but the sweat composition is always changing”

So, Halámek wants to apply this idea to the crime scene. Because people are always sweating, it’s easier to find sweat at a crime scene than it is to find fingerprints. Halámek’s team can use a strip they developed to pick up a sweat sample, and they claim to be able to do an analysis in minutes with less than a drop of sweat.

The idea isn’t that you can use sweat like DNA to track down an individual and match it. The exact amount of chemicals in sweat vary throughout the day, so that would be tricky. Instead, this method could be used to narrow down the possible suspects. Sweat spots can show whether there were one, two, or more people at the scene. We already know from some of Halámek’s previous research that you can use sweat to figure out gender (even in month-old samples). Now, his team is working to develop a “forensic toolbox”: they’re figuring out how to identify even more attributes from sweat, like gender, age, and food habits. “I hope to be able to one day analyze sweat at a crime scene and then say, ‘we are looking for someone who is tall, white, female, in very good physical shape’ or ‘an old male with liver disease,’” he says.

While the chemicals in sweat won’t help forensics experts match sweat to individuals, that very same feature means we can use sweat to unlock our mobile devices instead of passcodes, facial recognition, or even fingerprints. “Fingerprints remain the same and can be faked, but the sweat composition is always changing,” says Halámek. “So if I steal a sweat sample somehow, it will not be valid to unlock your phone after a few hours.”

How would this work? And if your sweat is always changing, how would you get back into your own phone? The key is that levels of chemicals in sweat change in predictable ways. When you get a new phone, you would touch it with your finger at various times of day, so that the phone learned the chemical analysis of your sweat at 2PM and 9PM. Over time and with enough data, an algorithm would learn how your sweat fluctuated, so it could tell whether it was you. Of course, it’s possible to trick this too, but it would take a lot more work.

The Air Force is interested in the patch to monitor hydration

To collect and analyze sweat, you need people to actually sweat. Phillip Simmers, a doctoral candidate in biomedical engineering at the University of Cincinnati, says that scientists can induce sweat by putting a dime-sized electrode (often made into a patch) on someone’s hand, adding a stimulant gel, and running a light current. After stimulating a spot on the skin for a few minutes, that spot will sweat for 24 hours. But as someone sweats, it dilutes the gel, making it difficult to reach the skin — which means it’s harder to estimate the right dose of gel and stimulate a very precise amount of sweat. Plus, as gel and sweat get mixed up, the sensors have more trouble analyzing just the sweat particles.

To address this issue, Simmers and his team developed a special membrane. (This research was recently published in the journal Biomicrofluidics.) Their membrane maintains almost all the original concentration of the gel even after a day — meaning that the gel and sweat don’t get mixed up. Simmers and colleagues are now trying to use the membrane on biosensors. His coauthors include University of Cincinnati bioengineer Jason Heikenfeld, who founded a startup named Eccrine Systems that aims to make advanced wearables that accurately monitor sweat.

Similarly, the organization NextFlex (which works with academics, companies, and the Department of Defense) has been working on sweat patches that can help monitor hydration and stress. This patch looks like a large bandage that sticks on the skin and has several layers, says Scott Miller, NextFlex’s director of strategic programs. It collects sweat and sends it to a sensor inside the bandage. The sensor can measure the level of whichever chemical is relevant, and then analyze and wirelessly send that information to another system.

The Air Force is interested in the patch to monitor hydration, according to Miller. “The entire Department of Defense has interests in looking at the hydration state of soldiers and airmen who end up becoming dehydrated and suffering health consequences in training and real-world scenarios,” he says. “Having a device that could allow a trainer or a staff sergeant to identify these people and help them take a break before they get injured would be really helpful.” Taken out of the defense context, it could be helpful in sports for athletes.

Another possibility is to use the patch to measure stress, or more accurately, monitor hormones such as cortisol that are linked to sweat. The most obvious application is to think of pilots in a cockpit, says Miller, but it could be aircraft mechanics, drone operators, students, anyone who works in a factory.

Traditionally, blood has been the gold standard for health monitoring, but it’s expensive and you need professors. Wearables like the Fitbit tell you when your heart rate is going up, but not more than that; it won’t tell you why. Sweat, on the other hand, doesn’t hurt to collect, and it still contains different hormones, proteins, and ions to detect disease. Additionally, sensors are being built to measure the contents of sweat, including blood sugar, which could one day help diabetics, and ethanol, which can tell if someone’s been drinking. It could be used to monitor the byproducts of medication to tell if someone hasn’t taken their medication in a while and remind them to do it. “There’s a lot of work being done in this area and a bunch of different sensors, and the possibilities are truly amazing,” Simmers says.