Understanding Sweat: The Hidden Insights

Welcome to Chasing Life and, I guess, to summertime. It’s that special time of year filled with barbecues, baseball games, and maybe just hanging out by the pool or lake—like I love to do back in Michigan. Summer is great, but it also means, well, heat. And for our bodies, that usually means sweating. Everyone sweats, some more than others, and there’s no reason to feel embarrassed about it. Sweat is actually our body’s way of cooling down. Recently, research has revealed that sweat does a lot more than just help us cool off. Each droplet might actually carry valuable information about our health, revealing insights about hydration, nutrient levels, and even kidney function. It’s pretty fascinating when you think about it. Today, I’ll be chatting with Professor John Rogers, who is leading much of this research. He’s the director of Northwestern’s Querry Simpson Institute for Bioelectronics and knows quite a bit about sweat. We’ll dive into what sweat is, its potential applications, and how it could truly improve health and performance. I’m Dr. Sanjay Gupta, and this is Chasing Life.

What Is Sweat Anyway?

So, what is sweat? Well, it’s a fluid produced by glands situated just beneath the skin’s surface. These glands connect to ducts that move sweat to the skin’s surface. Interestingly, there are a lot of sweat glands on fingertips—about 400 per square centimeter, which is quite high.

“On my fingertips? I had no idea,” I said, surprised.

“Yeah, if you take a close look at your fingertips, you’ll notice sweat pores on the ridges of your skin,” he explained. A lot of sweat can emerge from there. If you’re feeling nervous or exercising, sweaty palms can happen too. But there are sweat glands all over the body, not just on the fingers. The forehead has a dense cluster—around 150 per square centimeter. Other areas like the forearms and back have fewer glands. There are two types of sweat glands: eccrine and apocrine. The eccrine ones are more common, while apocrine glands have a different chemistry and are mainly found in areas like armpits.

Why Do We Sweat?

When most people think about sweating, the first thing that comes to mind is, “I’m hot, I sweat.” And yes, cooling down is indeed the primary reason—we sweat to maintain body temperature. Sweating kicks in when our core temperature exceeds a certain level, and factors like external temperature and humidity play a role in how much we sweat. Interestingly, nervousness can also trigger sweating. Ever been anxious in an interview? You probably sweated a bit.

“Are you sweating now?” I asked.

“Not yet. We’ll see how it goes,” he replied.

There are also certain foods that can induce sweating, right?

The Variability of Sweat

“So, you’ve mentioned a few reasons we sweat: to cool down, due to nervousness, and in response to food. Is the sweat different depending on what causes it?” I inquired.

“Mostly it’s similar, but the chemical makeup can vary based on how fast you’re sweating and how much you lose. If you sweat rapidly, for example, the chloride concentration can rise compared to slower sweating,” he said.

Then I wondered, “Is your sweat fundamentally the same as mine? Or is there variation?”

“There is a large variation in electrolyte levels among individuals, which is primarily genetic. But lifestyle choices can also influence it, like diet or exercise levels. Some basic biochemical markers in sweat, such as creatinine and urea, tend to align closely with levels in the blood,” he noted.

What’s In Sweat?

It’s important to understand why sweat shares certain biomarkers with blood. They both stem from interstitial fluid, which travels from blood through small vessels. When sweat glands are activated, they pull from this same fluid, which travels through skin layers to form sweat. We’ll talk about correlations, specifically whether biomarker levels in sweat mean the same as in blood. When I get blood drawn, they measure electrolytes like sodium, potassium, and chloride, and sometimes even cholesterol. So, what can we find in sweat?

“We look at electrolyte levels, which is crucial for athletes and workers in hot environments, plus chloride levels for cystic fibrosis diagnostics. We’re also investigating kidney health by examining creatinine and urea concentrations. Additionally, we’re assessing nutritional biomarkers—like vitamin D, vitamin C, calcium, zinc, and iron—to establish whether these levels correlate with blood. This is particularly exciting because quick assessments of nutritional balance could be achieved, which could help significantly, especially in lower-income regions where nutritional deficiencies in children can lead to long-term health issues,” he explained.

“We’ll take a quick break, but when we return, I’ll be in the hot seat!”

The Experiment

“Let’s see if you’ve started sweating,” he teased.

“They say, ‘never let them see you sweat,’ but I guess that’s about to change. Last year, I visited Professor John Rogers at his lab in Northwestern,” I told the audience.

“Welcome to our testing facility!” he said as we entered.

He mentioned that the goal of my visit was specific.

“We have a portable sauna here that will mimic a hot environment,” he explained, pointing to a small tent-like structure.

Inside that tent, the temperature reached about 135 degrees Fahrenheit, and the aim was to get me sweating—something I was already starting to do after about 15 minutes. While in the sauna, I wore a small patch his team developed, which stuck to my skin. The back of the patch had reservoir channels—essentially, it looked like a tiny semiconductor. When I sweat, these channels fill up and change color, reflecting different biomarker levels in my body. It was pretty cool to see that this was measuring things like ketones and chloride, levels which would typically require a blood test.

“Let’s check how much you’ve sweat,” he said, clearly intrigued as he peered at the devices attached to my arms.

“It’s starting to fill up. The chloride assay is showing a light pink, indicating a concentration around 10 to 15 millimolar—great job!”

I was merely sitting there, doing nothing, yet my sweat glands were certainly active.

“Collecting sweat for research has posed challenges,” I remarked, reflecting on how blood and urine have been studied extensively, whereas sweat had not received as much attention.

“Yeah, the difficulty lay in gathering clean, uncontaminated samples. Early methods were clumsy, involving devices that scraped the skin or absorbent pads that you’d peel away. There needed to be a better way to collect sweat reliably and accurately,” he pointed out. “Recently, though, we’ve made strides.”

Where Is This Heading?

“So, what’s next for sweat research?” I asked. “Are we going to see improvements in correlating blood and sweat data, potentially using machine learning?”

“Absolutely. Machine learning models will help us understand health conditions better by utilizing biophysical and biochemical data from sweat. I think we’re just at the tip of the iceberg,” he noted enthusiastically. “There’s already a natural correlation for many biomarkers. For instance, creatinine and urea match up well between sweat and blood. We’re also exploring micronutrients like vitamin C. The goal is to analyze what healthy nutrition looks like, which is particularly crucial for kids.”

“What about measuring lipids, like cholesterol or triglycerides, through sweat?” I probed further.

“We’re looking into cholesterol but haven’t found significant amounts yet. Cortisol is another interesting area; while concentrations are low, we’re submitting related studies,” he explained.

Practical Applications

“Are people currently using sweat analysis for health?” I asked.

“Yes, so here’s the deal: I’m involved with a startup that stemmed from our academic work. I don’t play a day-to-day role, but I’m on the board. The company, Epicore Biosystems, has partnered with major clients in sports and worker safety. In those areas, tracking sweat loss is vital, especially for hydration and performance. Knowing how much water and electrolytes have been lost can help prevent issues like cramping and injury during sports or labor,” he explained.

“Can I purchase a device?” I asked.

“Absolutely! You can find them at Dick’s Sporting Goods or order through the Gatorade website, typically around $10 for a pack of two,” he replied.

As he wrapped up, I couldn’t help but express my fascination: “It makes perfect sense that sweat can provide valuable health insights. It’s clear that your research is just the beginning.”

“Thank you for your interest and for having me on your podcast,” he said graciously.

“Have a great summer, Professor,” I added.

That was Professor John Rogers, Director of Northwestern’s Querry Simpson Institute for Bioelectronics. Chasing Life is a production of CNN Audio. Our podcast crew includes Eryn Mathewson, Jennifer Lai, Grace Walker, and others. Special thanks to CNN Health’s Ben Tinker and Nadia Kunang.