Temporary tattoos aren’t just for style anymore. Scientists have developed a new wearable sensor that looks and feels like a henna tattoo but can monitor electrical muscle activity and body temperature, too.

In a paper published Monday in Nature Nanotechnology, researchers described a new ultrathin, lightweight, breathable sensor constructed from nanoscale mesh, a spaghetti-like entanglement of fibers a thousand times thinner than a human hair. It can monitor vital signals over a long period of time without inflaming or irritating skin, a side effect of many current devices.

“We succeeded in completely removing the discomfort of wear,” said Takao Someya, a co-author of the paper and professor in the University of Tokyo’s Department of Electrical Engineering and Information Systems. “People cannot even feel the existence of our devices on their skin.”

Existing wearable electronics are often made from a form of polyester or rubber sheets, which get good readings, but don’t allow enough air to pass through. They prevent sweating and often cause itchiness, redness or other irritation, making them unsuitable for long-term use.