Thus far, the way most wearables have tapped into our biometric data has centred around the use of heart rate sensors. Your favorite fitness tracker or smartwatch, whether it be a Fitbit Alta HR or Apple Watch, has been harnessing optical sensor technology to churn out our BPM data and other heart rate based metrics.
From that, the hardware – plus a little bit of software magic – can tell you even more about your health. We already know companies are beginning to look into atrial fibrillation, and that's in addition to helping figure out calories burned and how you're sleeping.
Read this: What wearables will measure in the future
But what if there was another metric we could use to check in on our health? Well, there very well could be. Say hello to sweat-based wearables, which are being worked on in labs and future-focused technology firms all over the world right now.
But what do wearables that can tap into our sweat actually bring us, and when can we expect them to hit the mainstream? Here's what we've found out.
One of the most exciting things about wearables from a health perspective is that they can be used to non-invasively track your health. And, as it turns out, the medical field has been working on ways to non-invasively track your body for a long time now.
Essential reading: The lowdown on hydration monitoring wearables
The only new thing for the present is that companies are slowly figuring out how to miniaturise existing technology so that it can fit on your wrist and keep track of your health on the go, rather than in some lab in a hospital.
Sweat, obviously, would be a non-invasive way of keeping tabs on your health. No one needs to prick you or cut you open or anything like that. You simply sweat, and then a sensor tells you what you need to know. It's just as simple as the heart rate sensor, which is the de-facto health sensor on wearables at the moment.
You take that non-invasive sweetness and combine it with a simple fact: Sweat is essentially a secretion from a bunch of glands in your skin. There is something literally coming from the insides of your body onto the outside.
In fact, according to Eccrine Systems, a company that specialises in deriving data from sweat, the biomarkers you can check on in your sweat can be "directly correlated" with biomarkers from blood, long considered the gold standard for medical testing.
So not only would sweat be a non-invasive way to check on your body's health, it would likely be a high accurate way too, in the realm of blood in some areas – which is far more appealing than something like heart rate, which has a comparatively limited scope.
What data can we actually get from tracking sweat?
Sweat contains key biomarkers like glucose, sodium, lactate, potassium and protein. You can use these molecule metrics to look for signs of disease. For example, if you have glucose from sweat you can try to track diabetes, and even look into pre diabetes.
In fact, researchers at Stanford University and UC Berkeley have been looking into just that. Another molecule that you can track within sweat is chloride ions. A high level of chloride in your sweat can be a sign of cystic fibrosis. This isn't a new, revolutionary way to track that disease; medical practitioners have known about this link for a while now.
However, what would be new would be being able to use a wearable device to track those things. These metrics can also be used to tell us real-time information about how our body is feeling. Think about it like a temperature gauge for how things are going in our body.
Ali Javey, professor of electrical engineering and lead of its wearable project, explains that the idea of sweat-based wearables is "to have this thumbs-up or thumbs-down device that will give real-time information: it could provide an alarm that you need to take some medication, or that you're getting dehydrated and need to drink some water."
This is a fairly natural extension of why we sweat in the first place. Sweat is a natural alarm system. When our body is overheating, we produce sweat. When that sweat begins to evaporate, it is supposed to cool down our bodies just enough.
Who's working on it?
There are always the researchers. As previously mentioned, Stanford and UC Berkeley have partnered up to work on a fitness tracker-style wearable that would be able to analyse your sweat.
The University of Pennsylvania has combined those ideas with graphene, a material considered to be "the best sensor material in existence", to create the SweatSmart by GraphWear. Graphene would essentially allow the sweat sensor to be four times more accurate than current sensors.
Then there are companies like LVL and Halo Wearables, who are aiming a little lower with their sweat-based trackers. The company has spent the past six years working on the Halo Edge, a device that analyses your sweat to indicate hydration levels.
If you move away from the consumer space a little bit you get companies like Eccrine Systems, who are essentially building a sweat-based platform for wearable devices that can help athletes and employees of all types. However, it, and its sweatronics platform, are fully focused on B2B relationships.
In the same neighbourhood is Kenzen, which also has a focus on businesses. This company produces the Kenzen patch, which continually tracks biosensors in your sweat and sends you real-time alerts about your health.
What are the downsides?
Your heart is always beating, blood is always pumping through your veins. This means that heart rate sensors can give you constant snapshots of your life. You can see your heart rate when you're working out or sitting around or watching a movie.
Essential reading: How the Apple Watch heart rate monitor works
Sweat-based wearables, however, need sweat. The vast majority of people aren't constantly sweating either. You mostly sweat when you're working out or it's really hot out, while some people sweat when they get really nervous.
This obviously means that sweat-based wearables aren't as good at being the all-in-one solution for your entire day, from sleeping to going out and living your life.
When can we use it?
That depends on the person you are. The most advanced technology tends to start up high, with expensive price points and limited openings. Kenzen's Patch, for instance, will only ship 500 units at launch, and the company is still developing the product as of November 2017.
Eccrine Systems is signing deals with other companies for its technology to be put in devices, but there's no clear date on when any of those companies will actually launch. If you're a professional athlete or are in another field like that, it's likely these products will arrive in your world before that.
Researchers are developing several products, but when researchers develop products it often takes years for them to get off the ground – if they ever do. The most likely scenario is a startup comes along, takes the technology, finds a way to package it and brings it to market.
However, the best hope perhaps lies with LVL and Halo Wearables. There's a chance that bigger companies like Samsung, Apple and Fitbit will explore sweat-based wearables, but that doesn't seem to be on the horizon just yet. So it might be down to the startups to make the breakthrough first, and hope the major wearable tech heavyweights follow.