What Your Sweat Could Reveal About Your Health
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Welcome to Chasing Life and welcome to summertime. You know, it's that time of year. Barbecues, baseball games, the beach, lounging by the pool, maybe lounging by the lake like we do in my home state of Michigan.

I love summertime. But, you know, summertime also means heat, and for our bodies, that means sweat. We all sweat every day. Some of us more than others, yes, but nothing to be ashamed of. You certainly know that sweat is our body's natural cooling system. But there's been all this research recently telling us that sweat can do a lot more than just turn down our body's temperature.

Each droplet of sweat could be full of signs and signals about what's going on deep inside our bodies. Sweat could be the key to understanding not only our hydration, but also our nutrient levels, our kidney health. Sweat is a lot more fascinating than you probably ever realized. And today I'm sitting down with one of the scientists who's leading that research. His name is Professor John Rogers, and he is director of Northwestern's Query Simpson Institute for Bioelectronics.

He is an expert on sweat, and he's going to talk me through the basics of sweat, but also its potential, and help me understand how sweat could save a lot of lives and help us all perform at our very best. I'm Dr. Sanjay Gupta, CNN's chief medical correspondent, and this is Chasing Life. First of all, just some terms. What is sweat?

So sweat is a fluid created by glands that exist about a millimeter below the surface of the skin. These glands connect to ducts that transport sweat generated by the glands to the surface of the skin. The density of sweat glands is highest on the fingertips, about 400 glands per square centimeter. On your fingertips? On your fingertips, yeah. I didn't realize that. Yeah, if you look at sort of a magnified view of your fingertips,

The sweat pores exist on the upper surfaces of the ridges of the texture of the skin of the fingertips. So quite a lot of sweat will come out of your fingertips. You get sweaty palms, you know, you feel nervous or something like that. You're exercising. But you have also sweat glands distributed across your entire body, obviously not just your fingertips. There's pretty high density of sweat glands in your forehead.

about 150 sweat glands per square centimeter on your forearms.

maybe half of that on your back and your abdomen, that kind of thing. So there are two classes of sweat glands. One is called eccrine sweat glands, and those are the ones that I just referred to. There are other sweat glands that are a little bit different, and they involve a more complex chemistry associated with the sweat. Those are the apocrine glands. They exist, the armpits, the genital regions, and so on. Most people hear sweat, and they think, I get hot.

I sweat. That helps my body cool down. Is that the primary reason we sweat? Primarily, that is the reason for thermal regulation, so maintaining thermal homeostasis. So sweating is triggered when the core body temperature rises above a certain threshold.

And then the rate of sweating is determined by the external temperature and humidity level and so on. But sweating can also be induced by nervousness. There are sort of emotional cues that will cause a sweating. So if you're really nervous in an interview, you will start to sweat. Are you sweating now? Not yet. Yeah, we'll see how it goes.

And there are different kinds of foods that you can eat, right, that will cause sweat. Sure. So you mentioned three reasons that we sweat. To cool the body, when we may be nervous, and maybe in response to certain foods. Is the sweat different depending on what the stimulus for the sweat is? It's more or less the same, although the chemical composition of sweat can depend on sweat rate.

and the total volume of sweat that's been lost. So if you sweat very quickly, for example, at a high rate of sweating, the chloride concentration can be higher than at slow rates of sweating. So there are some dependencies there on the rate and the amount of sweat that's been lost, but not so much on the mechanism by which the sweat is induced.

Is your sweat fundamentally going to be similar to my sweat or how much variation is there from human to human? So there's a quite a large variation in the electrolyte level in sweat and that's just genetically determined. That's so much on your fitness level or how much you've sweat in the past. It can be modulated by that but there's sort of genetic baseline that determines you know your kind of average

electrolyte level, but it can be modulated by dietary habits, can be modulated by the amount of exercise you're doing, your fitness level, that kind of thing. But for more basic biochemical species, let's say creatinine and urea, which we'll talk about in a little bit in the context of kidney health, that tends, what we're seeing in the data is that those two biochemical species in sweat correlate very nicely with the same species in blood. Now I do want to take a moment here and explain a couple things.

First of all, the reason sweat carries the same biomarkers as blood is because they have something in common. Interstitial fluid.

Interstitial fluid comes from blood as it's traveling through small blood vessels or capillaries. It's found throughout the body, and its main function is to transport oxygen and other nutrients to cells and also remove waste from cells. But here's the thing. When sweat glands are activated, they are pulling from that same interstitial fluid, which then diffuses across layers of skin to become sweat.

The second thing, you're going to hear us talk a lot about the concept of correlation. Specifically, whether or not certain levels of biomarkers detected in sweat could have the same medical significance if found in blood. When I went to the doctor, got my blood drawn and everything, they're measuring basic chemistries, my sodium, my potassium, chloride, things like that. They might also measure my cholesterol and lipids and things like that. What can sweat measure?

So for the things that we're looking at specifically, it's electrolyte level, electrolyte replenishment becomes very important for athletes, for workers in oil and gas, manufacturing, construction, that kind of thing. Chloride for cystic fibrosis diagnostics, we published on that and we've done studies on large cohorts of infants.

Kidney health is one that we think is really interesting, looking at creatinine and urea concentrations in sweat, as I mentioned. We're also very interested in sweat, the nutritional biomarkers that are in sweat. So we have assays for vitamin D9, vitamin C, calcium, zinc, and iron.

And we're in the process of establishing whether those species in sweat also correlate with species in blood. That's ongoing work. But I think that would be very powerful because you would be able to assess nutritional balance very quickly, right? And I think especially in lower and middle income countries, nutritional deficiencies in pediatric patients can cause health challenges throughout an individual's life. We're going to take a quick break here, but when we come back...

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Last year, I decided to go pay Professor John Rogers a visit at his lab at Northwestern. All right, welcome to our testing facility. He had one goal for me. So we have a portable sauna here. It's going to replicate the environment that you would experience. That's right. In the lab was a portable sauna. Picture this small tent where your entire body is zipped in, except for your head. And then the temperature inside that tent is cranked up to a cozy, about 135 degrees Fahrenheit. And the whole

And the whole point is to get me to sweat, which you can probably see that I'm starting to do, having been in here for about 15 minutes. Now, while I was in the sauna, Professor Rogers had me wear this small patch that he and his team had designed. This patch sticks straight onto your skin, and then on the backside, there are these reservoir channels. If you're looking at it, it basically looks like a semiconductor.

Now, when a person sweats, or in this case when I sweat, the channels fill with that sweat and turns the patch different colors to correlate with different levels of biomarkers in your body. What is interesting though is that they're basically trying to measure sweat on my arms here. And you can tell on this one, for example, that I've started to sweat. You can see some sweat on my arm.

This is measuring all these different things, ketones, chloride, all these things that you'd normally get tested with a blood draw by sticking a needle in your arm. Now you don't need to be in there. Let's take a look and see if you've started sweating. I'm starting to feel it a little bit. Yeah, okay. About 12 minutes. Not much yet on that side. Why don't we check the other device? Okay.

So it's started to fill. There's chloride assays over here, so you're seeing a slight pink color, which means probably chloride concentration around 10 millimolar, 15, something in that range. Great job. Thank you. I sat here and did nothing, literally. Yeah, yeah. Well, your sweat glands did something. They're working. Finding a way to actually collect the sweat, that has been the key in studying it.

You know, I think it's sort of fascinating. I remember thinking this before I met you, but then sort of reflecting on it afterwards. This idea that we study blood. We have all sorts of different ways of imaging the body. Why weren't we studying sweat all along? It seems like an easy one to sort of study.

I think probably the reason why it hasn't sort of taken off earlier is it's just difficult to collect pristine, uncontaminated volumes of sweat. In the early days, you'd use like a device to kind of scrape along the surface of the skin, sort of collect enough sweat that you can get it into a

into a pipette or a syringe or a vial or something like that. The other way to do it is you have like an absorbent pad and a layer of tape on top of it and you kind of put it down and then you peel it off and wring the sweat out of the pad.

But kind of clumsy approaches overall. So I think that was kind of a missing element, kind of an engineering mechanism for collecting volumes of sweat in a very reliable, reproducible way. Was it just the, as you call it, the clumsiness that led to this sort of being understudied? Or do you think there was just so much inertia around blood and urine and things like that?

Well, probably a combination of both. You know, I do think there was sort of this missing capacity for collecting, you know, tiny volumes of sweat and manipulating those. There's no question that that did not exist prior to, you know, maybe 2016 or so. I see. So that was definitely a shift. The other thing may be a broader sort of...

societal change where there's a greater and greater appreciation of sort of continuous health monitoring using non-invasive sort of wearable devices, you know, whether that's a watch type device that goes on your wrist or something that goes on your finger. What we've been interested in is sort of soft skin adherent

patches, essentially, be placed on anatomically relevant locations of the body for measuring different conditions associated with patient care. And so maybe in that context, it just makes a lot more sense to think about sweat and the ability to kind of capture that biochemical information and sort of a continuous process

wearable sort of platform. You put it on, sweat enters in, the color develops, you take a smartphone camera, you snap a picture of the device, it does automated color extraction, and the color then calibrates to a specific concentration of those species. So that's the way our devices work. Very simple sort of single-use device construction is the way we have it set up.

So it's not a binary thing because it's not just color changing. You're actually then quantifying what that color means, it sounds like. Yeah, that's right. The vibrancy of that color, the depth of that color correlates directly to a specific concentration level in a continuous manner.

Is the real secret sauce here this figuring out of the microfluidics? Is that what you're alluding to? Yeah, from an engineering standpoint, that's it. But as you've pointed out, really establishing through sort of medical research, what are the correlations between sweat chemistry and blood chemistry? And that's a little bit kind of outside of the domain of the microfluidic device itself because you can, in principle, study those correlations with any kind of collection vehicle. I think the microfluidics allows that kind of reproducibility and...

precision in collecting pristine volumes of samples of sweat, but that's more kind of in a biology domain, figuring out those correlations. But then the engineering piece, I think it's already in place. Well, so when it comes to sweat, then, where do you think this is going to go? I mean, are you going to get better if you look at lots and lots of data, for example, blood data and sweat data?

And you have these huge machine learning models now. Will we get better at correlating sweat with blood so that sweat becomes more meaningful? Where is this heading, do you think? Well, that's a great point. I would say, you know, those kind of machine learning models are going to be important in really getting a very deep understanding of one's health condition from a combination of biophysical sensor analysis.

outputs, as well as some of this biochemical information that we're capturing through sweat, and you collect it all together, I think it's going to be a really powerful opportunity. So I think it's a really exciting area for the future. So I would say that. The other thing is a lot of these species just correlate in a very natural way. It doesn't really even require machine learning. Like creatinine and urea we were just talking about, caffeine, alcohol. I think

What we will find, we haven't completely proven this, there are a lot of micronutrients in sweat. Vitamin C, for example, a number of different essential minerals for a healthy diet appear in sweat as well. We're very interested in pediatric health in that context. You put on a patch, you do kind of almost a full panel analysis of specificities.

species relevant to a healthy nutrition. But I think there are enough reasons to be interested in sweat, again, biased perspective, that we're plenty motivated. We're going to continue no matter what. And I think it's a great discovery area in terms of the biology. And there are some immediate applications here that don't even require these correlations to be established. What about lipids?

could lipids potentially be measured through sweat like cholesterol or triglycerides? That's a good question. We're hoping for cholesterol. We haven't found substantial amounts of it. You know, cortisol is an interesting one. And we just submitted a new paper on sweat cortisol. As you mentioned, there's a good correlation there. The concentrations are super low. I mean, some of the challenge just is related to the

Very minute concentrations of some of these speed more of a kind of an engineering challenge. I guess what's 99% water It's only 1% of all of these different chemicals, you know Collected together. So they're very minute in in terms of their their presence but amino acids are there we can we can capture those I think it's a really interesting discovery space like we you know started talking about there just hasn't been a lot of work and

on sweat, but I think a lot of the pieces are there and we're pretty excited about it. So how has it been going? Are people using it for these purposes?

Well, so great question. So, you know, full disclosure, I'm involved in a startup company that has kind of spun out of the academic work that we do kind of in our university lab environment here. I don't have any day-to-day role. I don't have a consulting relationship, anything like that, but I am the board. So it's good to kind of disclose that. But the company is called Epicor Biosystems. And so they have a couple of large sort of

customers and business relationships, in sports and athletics, and in worker safety. So in those cases you don't have to worry about correlations to blood because you're tracking sweat loss as a mechanism for determining how much water you've lost as a result of an athletic competition, a training, or if you're in the oil and gas industry, you're working in a hot humid environment, you're just sweating.

And it also measures electrolyte loss via that same mechanism. And that's important for sports performance because it's well known that poor hydration can lead to cramping and injury and decreased levels of performance. And so the idea is these devices can provide a precise way to determine how much

body water you've lost as a result of sweating. And you can use that information to hydrate at appropriate levels. So avoid over-hydrating or under-hydrating. And by similar token, you can determine how much electrolyte supplement salt tablets you need to take in order to get back to where you were before you lost electrolytes by sweating. And so they have a joint product offering with Gatorade. I don't want to pitch

Pitch products, but you ask, and so I think they've done about 3 million of these Gatorade GX patches, and there's an app that goes along with the patch. It works exactly the same way that I was just describing. It's a sticker. You put it on, and the channels fill with sweat. You can determine the extent of filling, and then there's a colorimetric reagent, in this case, that responds to chloride.

concentration, which is pretty much electrostatically balanced with sodium. So it's a good indicator of overall electrolyte concentration. And with the electrolyte concentration, you determine electrolyte loss. And so that guides replenishment. But if I wanted to buy one, could I buy one? Yeah, you can buy them. You can buy them at Dick's Sporting Goods. You can order them off of the Gatorade website. They're bundled in many cases with the GX bottles and the pods and that whole thing. So I think they're about

$10 for a pack of two kind of in that range. Well, you know, I just got to say again, when I first heard about your work, it made so much intuitive sense to me that you have sweat as a biofluid and

from which we can learn a lot of things about someone's health. And it seems like you've just taken it further and further. It's fascinating to me. It seems to me that it'll just continue to grow. I appreciate your interest and appreciate you having me on your podcast. Absolutely. Have a great summer, Professor. Thank you. Okay. Thanks a lot. That was Professor John Rogers, Director of Northwestern's Query Simpson Institute for Bioelectronics.

Chasing Life is a production of CNN Audio. Our podcast is produced by Aaron Mathewson, Jennifer Lai, Grace Walker, Lori Gallaretta, Jesse Remedios, Sophia Sanchez, and Kira Dering. Andrea Kane is our medical writer. Our senior producer is Dan Bloom. Amanda Seeley is our showrunner. Dan DeZula is our technical director. And the executive producer of CNN Audio is Steve Liktai.

With support from Jamis Andrest, John D'Onora, Haley Thomas, Alex Manasseri, Robert Mathers, Lainey Steinhardt, Nicole Pesereau, and Lisa Namarow. Special thanks to Ben Tinker and Nadia Kanang of CNN Health and Katie Hinman.

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