It’s no secret that life can get rough. Those who have to contend with that for too long can start feeling overwhelmed — burned out by the stress. Now, a team of researchers proposes a new approach through which we can quantify how much stress someone is under, and for how long. They hope that the new wearable device can help prevent burnout, and let us know when someone is most in need of support or a good old fashioned break from the stress.

The new device was designed by a team of engineers at Ecole Polytechnique Fédérale de Lausanne (EPFL) Nanoelectronic Devices Laboratory (Nanolab) and Xsensio, a Swiss-based biotech company. It takes the shape of a wearable sensor that measures the levels of the stress hormone cortisol in a person’s sweat. This figure can then be used to gauge the levels of cortisol in the blood.

The sensor is placed directly on the skin and provides continuous readings of this hormone’s levels in their sweat.

Skin-deep stress

“Cortisol can be secreted on impulse — you feel fine and suddenly something happens that puts you under stress, and your body starts producing more of the hormone,” says Adrian Ionescu, head of Nanolab.

“But in people who suffer from stress-related diseases, this circadian rhythm is completely thrown off. If the body makes too much or not enough cortisol, that can seriously damage an individual’s health, potentially leading to obesity, cardiovascular disease, depression or burnout.”

Cortisol is synthesized from cholesterol in our body’s adrenal glands — these sit right on top of your kidneys. How much of it is secreted is in turn controlled by the pituitary gland in our brains through the use of the adrenocorticotropic hormone (ACTH).

It’s easy to read “stress hormone” and immediately assume cortisol is a bad guy, but that’s simply not true. As we’ve seen previously, stress is a completely natural and deeply useful response; the issue with it today is that we’re feeling much more stress than we would in our natural environment. In other words, stress isn’t the issue — too much stress is.

In our day-to-day, cortisol has some very important functions, including keeping our metabolism, blood sugar, and blood pressure in check. It’s also deeply involved in other cardiovascular functions and the workings of the immune system. In a stressful situation, be it something life-threatening or a simple annoyance, cortisol is flooded into the body to make us ready for our ‘fight or flight’ response. This mostly means prepping up our brain, muscles, and heart for intense activity and possible injury.

Still, cortisol levels in the blood ebb and flow naturally throughout the day, following our circadian rhythm, to keep us functional or asleep as needed. It generally peaks between 6 am and 8 am to rouse us from sleep and then decreases gradually.

Since cortisol is such a good marker of how stressed we feel and how stressed our body actually is, it’s often used as a gold standard to gauge stress. But it gets even trickier: in addition to all this variation, cortisol also counteracts insulin and contributes to hyperglycemia. Viral infection, traumatic events, and other severe effects can also cause the cortisol level to shift.

In order to measure the cortisol level, you need to take a blood or urine sample, and those aren’t something you can take just anywhere throughout your day. Furthermore, the cortisol test results depend on the sample type (blood or urine), the method used for sampling, and other health parameters. Results of individual tests should must be interpreted with care, depending on this context and using a lab reference range.

With this in mind, the team designed a wearable sensor to measure how much cortisol an individual excretes through their skin. It contains a transistor and a graphene electrode, which the authors explain has very high sensitivity and can detect even low levels of the hormone. Aptamers, short fragments of single-stranded DNA or RNA that can bind to specific compounds, are tied to this graphene electrode, allowing it to interact with the cortisol molecule. Since the aptamers used naturally contain a negative charge, they will be electrostatically attracted to the cortisol molecule and release a charge as they bind together.

The more such molecules are present, the stronger the overall charge becomes. This allows for accurate and direct measurement of its levels in sweat. The authors explain that this is the first device intended to continuously monitor cortisol levels throughout the circadian cycle (i.e. throughout the day).

“That’s the key advantage and innovative feature of our device. Because it can be worn, scientists can collect quantitative, objective data on certain stress-related diseases. And they can do so in a non-invasive, precise and instantaneous manner over the full range of cortisol concentrations in human sweat,” adds Ionescu.

They tested the device in the lab and found it reliable and efficient; the next step is to now make it available for healthcare workers or researchers. They’ve set up a bridge project with Prof. Nelly Pitteloud, chief of endocrinology, diabetes, and metabolism at the Lausanne University Hospital (CHUV), where the device will be tested for continuous use in a real-life hospital setting. They intend to run the test using healthy individuals as well as patients with Cushing’s syndrome (who produce too much cortisol), Addison’s disease (too little cortisol), and stress-related obesity.

As far as the psychological ramifications of stress, the team explains that they are still “assessed based only on patients’ perceptions and states of mind, which are often subjective”. A system such as this patch can help us determine quite reliably how much cortisol is running through their system, which can be used to gauge those at risk of depression or burnout. If nothing else, it will help them support their claims with cold-hard figures.

The paper “Extended gate field-effect-transistor for sensing cortisol stress hormone” has been published in the journal Communications Materials.