Cortisol is a steroid hormone released by the adrenal glands. Often called the “stress hormone,” cortisol levels generally increase when a person is under stress. Measuring cortisol can help diagnose Cushing syndrome, adrenal or pituitary conditions, and Addison disease, according to Lab Tests Online. Also, high cortisol levels can interfere with memory and learning, can lower bone density, and can affect the immune system. Cortisol levels rise and fall during the day which makes them difficult to measure with a standard blood test.

Materials scientists at Stanford University’s Salleo Lab developed a wearable biosensor patch that quickly measures cortisol levels in human sweat. The stretchy patch adheres to the skin and wicks up the sweat which then passes through into a small pool. A membrane that binds only to cortisol covers the pool and acts as the biosensor. Sweat contains charged ions such as sodium and potassium which would pass through the membrane unless blocked by the cortisol. Cortisol itself has no charge, which means typical biosensors cannot detect its presence. However, the Stanford device can read the charged ions from the other elements that are stuck in the membrane due to the presence of cortisol, providing an indirect way to infer cortisol levels. For a fast cortisol reading, all that’s required is to stick the patch on slightly sweaty skin.

Science Advances published a paper explaining the wearable cortisol sensing patch in July. The wearable produces similar results to the current gold standard clinical test in the lab and real-world tests, the Stanford scientists say. Next steps in development are to make the sensor more accurate, more reliable, and reusable. Future developments include testing the sensor with saliva, which would mean patients would not need to work up a sweat.