Someday soon, perhaps within a year, you’ll be able to slap a soft, stretchy patch on to your arm that tells you if you’re dehydrated. Or that your electrolytes are dangerously out of balance. Or even that you have diabetes. Fitness trackers such as Fitbit and Apple Watch already track step counts, heart rate and sleep rhythms. But they tend to be rigid and bulky, and mostly gather mechanical metrics, rather than assess a person’sunderlying biology.

A new generation of devices instead aim to analyze sweat for many chemicals at once, producing a real-time snapshot of the wearer’s health or fitness. These devices also fit intimately against the skin, and are comfortable for anyone, from premature babies to the elderly. One version is already being advertised by Gatorade. The latest advance in this technology, described Friday in the journal Science Advances, provides real-time information on the wearer’s pH, sweat rate, and levels of chloride, glucose and lactate — high levels of which could signal cystic fibrosis, diabetes or a lack of oxygen.

“It fits into a broader trend that you’re seeing in medicine, which is personalized, tailored approaches to treatment and delivery of care,” said John Rogers, a biomedical engineer at Northwestern University in Illinois and the key architect of the device. Technology like this has been anticipated for years, but the field has accelerated rapidly. Some similar devices in development are soft. Some use electric sensors to read chemicals. Others rely on colorimetrics, in which the intensity of the color in the readout matches the concentration of the chemical being monitored. The new device delivers all of that in a battery-free and wireless form.

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