PhotoTat: Ink That Turns On and Off

There is a particular appeal in the idea of a tattoo that is not permanent—not because the wearer regrets it, but because the nature of self-expression is not always fixed. The things we want to say about ourselves on a Tuesday may not be the things we want to say on a Friday, or in a boardroom, or at a family dinner. A new technology from the University of Colorado Boulder suggests that tattoos may soon become as changeable as the moods and moments they represent.

The technology is called PhotoTat, and it uses light-sensitive dyes encapsulated in tiny spheres of polymethyl methacrylate—a transparent plastic better known as plexiglass—to create tattoo inks that are nearly invisible under ordinary light but burst into vivid color when exposed to ultraviolet light. The colors fade over several hours, or can be switched off faster with bright visible light. The inks were described in a study published in the Cell Press journal Matter & Light in October 2026.

“PhotoTat is like a switch,” said lead researcher Carson Bruns, an associate professor at CU Boulder. “You turn it on with UV light, but you can turn it off again when you go to grandma’s house”. Bruns, who has tattoos of his own, has tested the inks on himself. He has a black outline of fish scales on his leg, which he fills in with PhotoTat inks. With a little light, he can turn those scales red, orange, blue, and more—what he calls “magical mermaid scales”.

The technology works through a class of chemicals called photochromic dyes, which change color when exposed to specific wavelengths of light. The researchers encapsulated three commercially available dyes in PMMA spheres, each a few hundred nanometers across. The dyes produce blue, magenta, and yellow, which can be combined to create a wide range of colors. It takes about two to three seconds of bright UV light to activate the pigments, and the same amount of visible light to deactivate them.

Beyond the cosmetic applications, Bruns sees practical uses for the technology. Many patients undergoing radiation therapy receive small permanent tattoos to help doctors align radiation beams. “They’re not beautiful, and they become a permanent reminder of a traumatic experience,” Bruns said. “With PhotoTat, we could turn an involuntary medical tattoo into something that’s only visible to the doctor when you go in the clinic, and then it can be invisible the rest of the time”.

The technology is not yet ready for commercial use. The blue dye is not a true cyan, limiting the range of hues that can be created. The blue also loses its switchability over time, eventually leaving a permanent purplish color. And while PMMA has a history of medical use, the specific PhotoTat formulations still need independent safety testing before they could be considered for widespread use.

Bruns has had his PhotoTat tattoos for more than two years, and they remain responsive to light. But one person’s experience cannot establish safety for the broader population. The inks remain a laboratory curiosity for now—a promise of a future in which the marks we choose to make on our bodies are as fluid as the selves we bring to the world.

AI Image Disclaimer: The visual content in this article was generated using artificial intelligence for illustrative purposes only and does not depict the actual inks or individuals described.

Sources: EurekAlert, C&EN, New Atlas, Yahoo Tech, Matter & Light