You are born with up to 4m sweat glands to provide a natural way to regulate temperature. The evaporation of perspiration cools you down. As sweat is produced it also picks up a lot of information about how the body is behaving, in the form of “biomarkers”: electrolytes, sugars, amino acids, proteins, hormones and many other molecules that are the products of metabolism. If the tiny traces of these substances can be detected and measured, then it should be possible to monitor a person’s health from his sweat.
One of the biggest uses may be to monitor blood-sugar levels in people with diabetes. At present, diabetics must prick a finger regularly to obtain a drop of blood, testing it on an electrochemical strip inserted into a meter that calculates the amount of glucose in the blood. Some patch systems already exist, but tend to rely on microneedles, which continuously sample blood and transmit the results to a wearable device via a wire.
If Jason Heikenfeld of Eccrine Systems, a Cincinnati firm, has his way, the days are numbered for pricking the skin to obtain a sample. Dr Heikenfeld is trying to develop a sweat sensor to do the same job. What makes that possible is better understanding of biomarkers themselves—there are some 800 in sweat—and advances in “microfluidics”, a technology which uses minuscule pipes, valves and sensors to manipulate and test minute amounts of liquid.
The patch that Eccrine Systems is developing absorbs sweat from a porous adhesive to the sensor, which is coated with a membrane that attracts a specific biomarker for measuring glucose. A microprocessor then determines the concentration and transmits the data wirelessly. A disposable sweat patch for glucose monitoring could be worn for as long as a week, allowing round-the-clock monitoring. The data could also be relayed directly to a doctor.
Gentag, based in Washington, DC, announced a prototype diabetes patch in July. John Peeters, the chief executive, says it too will relay information to a device wirelessly. Both Gentag and Eccrine Systems aim to have their patches on the market in 2016.
The World Health Organisation says diabetes affected 387m adults worldwide in 2014 and expects that number to exceed 590m by 2035. Sufferers are likely to require two to three times as much health-care spending as healthy individuals. Since this burden could be greatly alleviated by prevention and monitoring, it is a problem worth sweating over.