Purdue University researchers have developed a low-cost skin patch that changes color to indicate different levels of hydration. The device could potentially be used by marathon runners, military personnel and others to help prevent illness arising from lack of fluid intake.

“Hydration in humans is a delicate parameter,” says Babak Ziaie, professor of biomedical engineering and electrical and computer engineering. “Even small deviations such as 2% from normal levels can affect a person’s cognitive and physical performance by more than 30%.”

The palm-size patch consists of filter paper that is laser-machined to As sweat secretion increases, the strips are activated sequentially, changing from blue to red to indicate levels of moisture loss. Image credit: Purdue University/Vaibhav Jain, Manuel Ochoa.create a radial array of strips, which are laminated with a water-impermeable film to form microchannels. The channels are loaded with a water-activated dye at one end. As sweat secretion increases, the strips are activated sequentially, changing from blue to red and providing easily identifiable levels of moisture loss.

Ziaie says that the patch was tested over a square centimeter of skin at a sweating rate of 90 microliters per hour, which corresponds to normal human perspiration rates.

Conventional methods for monitoring hydration are either invasive, require non-portable equipment or do not yield results immediately. In comparison, Ziaie says, the patch is fast and user friendly—and its fabrication process could be scaled up to large-volume manufacturing.