New PhotoTat Inks Let You Turn Tattoos On and Off With Light

Researchers at the University of Colorado Boulder have developed a rewritable, light-sensitive tattoo ink called PhotoTat that allows users to switch body art on and off using different wavelengths of light, nine.com.au reported on October 10, 2026. The technology utilizes photochromic dyes enclosed in medical-grade nanoparticles, enabling temporary tattoos that fade under ultraviolet light or disappear rapidly when exposed to bright outdoor sunlight or an LED light.

How PhotoTat Inks Work Under Light

PhotoTat is formulated using polymethyl methacrylate, or PMMA, which forms tiny glass-like spheres that encapsulate light-sensitive compounds known as photochromic dyes. According to reporting from Live Science, mixing primary colors of blue, magenta, and yellow allows researchers to generate full-color images beneath the skin.

Exposure to a 365-nanometer ultraviolet LED activates the pigments in approximately two to three seconds. Once turned on, the colors persist for hours or even days under typical indoor lighting before fading. Users can also switch off the design faster by shining a bright LED light or walking out into the intense outdoor sun, which erases the appearance in seconds while leaving the pigment inside the skin.

Medical Applications for Radiation Therapy

Beyond cosmetic adjustments like concealing body art for job interviews, lead author Carson Bruns highlighted potential clinical uses for the technology. Patients undergoing radiation therapy often receive permanent tattoos to guide radiation beams, which can serve as a lifelong reminder of a traumatic medical experience.

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.

Carson Bruns

Commercial Availability and Safety Testing

The technology remains strictly off the market while researchers evaluate its long-term viability. Live Science noted that tests across all three PhotoTat channels showed the pigments remained switchable in human skin for between 1.4 and 2.2 years.

While Bruns has experimented on himself as part of the ongoing research, formal safety determinations for human use have not yet been finalized. The team’s findings were published on October 9, 2026, in the Cell Press journal Matter & Light.