Wearable gauges fitness through stress hormones in your sweat

Stanford's device tracks cortisol levels at the very moment they're relevant.

Cortisol (best known as the stress hormone) is handy for tracking your athletic performance and even spotting signs of disease, since it reflects how well your adrenal or pituitary glands are working. But there's a problem: measuring that often takes several days of lab work, by which point the info is no longer relevant. Scientists might have a much better option. They've developed a flexible, wearable sweat sensor (not shown here) that tracks cortisol levels with results in seconds -- that is, while it's at its most useful. It sounds straightforward, but the team had to overcome a major obstacle common to most biological sensors.

A typical sensor looks for the positive or negative charge in molecules, but that's not really an option with a chargeless substance like cortisol. The researchers tackled this with a membrane that binds only to cortisol and lets regular charged molecules pass through. The sensor then measures the cortisol-carrying molecules trapped by the membrane, rather than the cortisol itself. All you need to do is visibly sweat and apply the patch.

The technology isn't perfect in its current incarnation. It can work multiple times, but it struggles if bogged down in sweat. They also want to improve the overall reliability and try using it on your saliva, saving you from having to work out to gather data. Nonetheless, the potential is clear. This could help sports stars and fitness mavens quantify their abilities mere moments after finishing a sweaty workout, and it might provide clues to otherwise imperceptible illnesses.