Scientists have developed a waterproof wearable patch, which when applied directly to the skin, absorbs sweat and within seconds assesses how much cortisol -- stress hormone -- a person is producing.

Clinical tests that measure cortisol, which rises and falls naturally throughout the day, provide an objective gauge of emotional or physical stress and can help doctors tell if a patient's adrenal or pituitary gland is working properly. While current methods require waiting several days for results from a lab, with the novel patch, a user just needs to sweat enough to glisten, apply the patch and connect it to a device for analysis, giving the results within seconds.

"We are particularly interested in sweat sensing, because it offers non-invasive and continuous monitoring of various biomarkers for a range of physiological conditions," said lead author, Onur Parlak from Stanford University, US. "This offers a novel approach for the early detection of various diseases and evaluation of sports performance," Parlak added, in the paper published in the journal Science Advances.

If the prototype version of the wearable device becomes a reality, it could allow people with an imbalance to monitor their own levels at home, the researchers said. A fast-working test like this may also reveal the emotional state of young, even non-verbal, children who might not otherwise be able to communicate that they feel stress, they noted. The team developed a stretchy, rectangular sensor around a membrane that specifically binds only to cortisol. Stuck to the skin, it sucks in sweat passively through holes in the bottom of the patch. A waterproof layer protects the patch from contamination.

The sweat pools in a reservoir, which is topped by the cortisol-sensitive membrane. Charged ions like sodium or potassium, also found in sweat, pass through the membrane unless they are blocked by cortisol. It's those backed up charged ions the sensor detects, not the cortisol itself.