A new skin patch could help you keep tabs on your health while you work up a sweat — literally.

Key points: Flexible stick-on patch measures pH, lactate, glucose and chloride ions in sweat

Flexible stick-on patch measures pH, lactate, glucose and chloride ions in sweat Colour changes on patch analysed using smartphone app

Colour changes on patch analysed using smartphone app Patch could be used to measure athletic performance and health conditions

An international team of scientists has developed the first stick-on patch that analyses sweat to provide detailed information about dehydration, electrolyte, sweat rate, and fatigue levels, they report in the journal Science Translational Medicine.

"Sweat is rich in body chemistry that can provide insights into health, fitness and physiological state," said John Rogers, a professor of material science engineering at Northwestern University, who was part of the research team that helped develop the device.

"[This device can] monitor patterns of exercise, helping people determine when they may need to rehydrate, when their electrolyte composition is getting out of balance, when they're getting into anaerobic regimes of exercise," he said.

Colour-coded chemicals

The circular device — about the size of a 10-cent coin — has four indicators that measure lactate, glucose, chloride ions and the sweat's pH.

"pH is a good indicator of overall hydration levels. Chloride is a key electrolyte that's lost during the process of sweating, so generally those electrolytes have to be replenished," Dr Rogers said.

The colour of the chemicals in the device change depending on the composition and concentration of those chemicals in a person's sweat.

These colour changes, and sweat levels indicated by changes in a squiggly channel, are then captured and analysed by a smartphone app that connects with the patch wirelessly.

Professor Rogers said the new device was better than the current technique for measuring sweat loss, which involves taping fabric to a person's body, letting it soak up sweat, then weighing it to find out how much has been produced.

"It makes the process of sweat analysis a lot more quantitative, a lot more reproducible, and from the standpoint of the individual, just a lot easier to accomplish," he said.

Like a second skin

The patch could come to market within a year, according to Professor Rogers ( J. Rogers, Northwestern University )

Professor Rogers said the team had worked through several challenges to get the device to where it is today — most notably developing something that was compatible with skin and stayed on during rigorous exercise.

"Implementing it into materials that are biocompatible, they're non-irritating and comfortable, there were a lot of those things that we had to work through," he said.

The device was tested in nine healthy volunteers cycling in the lab as well as 12 cyclists participating in a long-distance outdoor race.

The researchers found the devices stayed in place for without causing any discomfort or irritation

"We've engineered these devices to have skin-like softness, compliance and flexibility. So you don't get any mechanically induced irritation or abrasion," Professor Rogers said.

Hopes for one-year timeframe to market

Now these obstacles have been worked through, Professor Rogers predicted the sweat patch would be commercially available soon.

"I don't think it's a three- to five-year timeframe, I hope it'll be much sooner than that, a one-year timeframe, but we'll have to see," he said.

The team envisaged the patch as a low-cost, single-use device to be used for a couple of hours and then disposed of.

"We want to keep it under a couple of bucks, the lower the better. If it's more than $1 or $2 the utility is significantly compromised," Professor Rogers said.

And while the fitness and wellbeing industry may be an obvious path for the device, Professor Rogers said there may also be medical applications for the patch down the track.

"We're attempting to use this patch as a platform for doing glucose detection in the sweat, then establish a relation between glucose in the sweat and glucose in the blood, and then use this device as an early pre-screen for determining glucose levels in diabetics," he said.