The Rise of Wearable Sweat Sensors

Since health wearables came onto the scene, they have been getting smaller, more discrete, and less invasive. While a fashionable wristband can monitor your heart rate, fitness levels and sleep patterns, a discrete device worn against the leg can now reduce painful symptoms of chronic illnesses.

The tiny self-adhesive sweat sensors that are being studied at the Northwestern University's Center for Bio-Integrated Electronics take this non-invasive approach to monitoring health one step further, with a barely-visible sticker capturing information about health via sweat from the skin, and reporting it back to a smartphone.

Not only are these wearable sensors smaller and less noticeable than their predecessors - they also give an even clearer picture of overall wellbeing, with researchers suggesting that they could one day be used in place of blood tests.

How does it work?

At face value, the 2.5cm-wide circular patch is little more than a soft, transparent sticker. It can be stuck either on the forearm or on the back. Suspended within the sticker’s gel-like consistency is an electric sensor, with four separate units each capable of measuring a different biomarker.

The device’s simplicity is only skin-deep, however. When sweat from the skin touches the sensor, chemical reactions cause the units to change colour based on the sweat’s pH, glucose concentration, chloride levels and lactate levels.

In its current incarnation, the patch requires the user to then take a photograph of it via the companion smartphone app, which then determines what the colours mean and presents the information in a comprehensive way.

Another fitness wearable?

The most commonly cited use for the sensor is showing how users respond to exercise, including whether they need to drink more water or replenish electrolytes. For professional athletes or those training in extreme conditions, having this information to hand could prove highly useful.

To that end, the sweat sensor has primarily been tested in athletic situations, with trials conducted on cyclists and runners. The athletes reported that the patches stayed firmly attached and didn’t cause any irritation during the trials, implying that they could be discreetly used during day-to-day life without any major inconvenience.

The clinical question

Perhaps more importantly, the data from the wearable sensors and their companion app were of equal quality to that taken from lab measuring techniques. This suggests that, with appropriate FDA approval, these non-invasive patches could slowly replace conventional tests for biological signifiers, and even be used as part of clinical trials.

Doctors have already used the information given by sweat to diagnose certain diseases and discover drug use, so this non-invasive and seemingly reliable step forward could make sweat tests as common as blood tests for certain conditions.

A step forward for patient retention?

Instead of needing to travel back and forth to a site of study for laboratory blood testing, trial participants may one day be able to monitor their own reactions to treatment via an unobtrusive sweat sensor and transfer the data to doctors via the companion app.

This would not only offer study facilitators regular and reliable health updates, it would also allow participants to continue their day-to-day lives relatively unimpeded. The comparative convenience of sweat sensor wearables would negate concerns that patients have over travel costs and time-consuming appointments, and could boost participation and retention.

Professor John A Rogers, who headed up the study, suggests that in the future the device can also be used to test patients for diseases such as diabetes and cystic fibrosis, offering instant results without the need for blood tests.

What’s next for the device?

The researchers intend to initially launch the device commercially for fitness and wellness use. The patches will be for individual one-time use, and will hopefully not cost more than $1.50 per device.

Plans are also underway for the device to be used with diabetes patients, allowing them to personally track the glucose in their sweat at any time, and assume more control over their intake.

Researchers have also entered into discussion with the U.S. Air Force, potentially using the devices to remotely track the health states of active-duty airmen.

With potential for this sweat-sensing technology to extend to other bodily fluids, such as tears and saliva, this device has opened a door for discrete one-time use wearables to enter the clinical market and change the way we look at gathering patient data.

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