When L’Oreal pitches you on its new wearable, you envision a Wi-Fi-connected makeup compact or some sort of skin-toning helmet. Or maybe a lipstick tube that’s also a USB stick. What you don’t envision is a sticker—a temporary tattoo with teeny, tiny circuits inside.

The beauty company has its own tech incubator, run by L’Oreal tech guru Guive Balooch. His team partnered with sensor-maker MC10 and design firm PCH to create a wearable called the My UV Patch. It attaches directly to your skin and measures UV exposure, relaying the information back to an app. You access the app by scanning the sticker (using NFC or your phone’s camera), which you obviously want to put somewhere the sun will indeed shine. The app gives you information about your UV exposure, using a pattern of blocks of color made of photosensitive dyes that measure your baseline skin tone and change colors when you’re out in the sun, depending on its strength.

You apply it like any other sticker, except this one hangs around a little longer—three to five days, usually. A few activity trackers and even more specific wearables measure UV to tell people whether they’re getting too much or too little sunlight, but not a lot of people are going to wear a Fitbit for UV health. A temporary sticker? Maybe. The app is cute and easy to use, and skin health is an important thing to monitor. But by far what’s most interesting about the product is that it’s one of the first flexible, skin-adhesive wearables that has a shot at a mainstream market.

They’ve Got Skin Covered

The idea of “smart” temporary tattoos isn’t a new one, but most projects have been highly conceptual, or without a practical purpose (other than attaching sensors to your body). But the work these three companies have done might finally push this type of product into consumer’s line of vision.

This is in no small part thanks to the advancements being made by healthcare technology company MC10, which specializes in flexible technology and tiny circuits. “We’ve been working on that for about six or seven years,” says Roozbeh Ghaffari, VP of Technology and cofounder of the company. “The partnership with Guive and L’Oreal really identified an area around skin health where this technology could have value—not just like, cool stuff in a material science lab.”

Not to say there weren’t challenges: MC10 and PCH (which worked on the manufacturing side) worried about causing skin redness or irritation, about how to create something that would just fall apart under water while wearers were showering. And then of course, how do you build such tiny circuits without breaking them? It’s hard to imagine packing NFC coil technology, an antenna, and circuits into something that’s flatter than flat. It’s stuck to my hand right now, and aside from the blue-patterned heart, it looks a part of it. While MC10 didn’t get into the details of how exactly they made all that so small what, (“thinner than a strand of hair”), each demo worked exactly as it was supposed to, and there’s plenty that this feat in miniaturization can be used for in the future.

My UV Patch will be available for free in the early Spring in 15 countries, and it will be entirely free…which makes it feel like something of a experimental product versus the first actually wearable wearable on the market. And there are certainly hurdles to be addressed—FDA approval, for one, and if people are still having a hard time getting on board with smartwatches, smart skin might take a minute.

More here:

How L’Oreal Built a UV-Measuring Temporary Tattoo