New tattoo inks can be switched on with UV light and fade in sunlight within seconds

A 365-nanometer ultraviolet LED can switch a tattoo pigment on in about two to three seconds, and bright sunlight erases the color again within seconds, even though the pigment stays in the skin. That is the behavior reported for a set of photochromic tattoo inks from a University of Colorado Boulder lab, published on 9 October 2026 in the journal Matter & Light.

Carson Bruns, an associate professor of biomedical engineering at the university, led the work with Mollie Stockton, Emily Gardner and Hyejin Kwon. The inks come in three colors, blue, magenta and yellow, and under indoor lighting the colors stay on for hours to days.

Photochromic dyes inside plastic nanoparticles

According to Live Science’s report on the paper, the three channels use photochromic dyes encapsulated in nanoparticles of PMMA, a medical-grade plastic already used in implants and dermal fillers. A photochromic dye changes between a colorless and a colored form when exposed to specific light. In the reported system the 365 nm LED flips the pigments to their colored state in roughly two to three seconds, and per the article the magenta channel responds to green light and the yellow channel to blue light.

Bruns has built toward this for years. In a CU Boulder Today profile from December 2018, he and then-graduate student Jesse Butterfield described dyes encased in plastic microcapsules, several times thinner than a human hair, that protect the dye while letting it sense changes. The capsules could be injected with the same needles tattoo artists use, and one early prototype was a “solar freckle” that shows up only under ultraviolet light. Bruns told the university at the time that sunscreen laid over such a mark would make it vanish even in sunlight, and the profile noted that the tattoos would need rigorous safety testing before use on people and were unlikely to be widely available for several years. Bruns tried a solar freckle on his own forearm first. He said he wanted to see whether it worked.

Sunlight as the off switch

Sunlight does the work that a second device would otherwise have to do. UV light of the right wavelength turns the dyes on, and bright sunlight turns them off, so the tattoo responds to light alone rather than to any electronics in or on the skin.

The off switch is the part that gives the inks their appeal. Bright outdoor sunlight erases the colors within seconds, while the pigment itself remains in the skin and can be switched on again. Bruns describes the result as a tattoo that can simply be turned off, and says the ink can be combined with conventional permanent ink in a single design, so a permanent outline could sit beside switchable fill.

His group’s earlier ink took the opposite approach. The ATLAS Institute’s page on the lab’s smart tattoos describes a mark that turns blue in sunshine or other UV light and disappears with sunscreen or indoor lighting, lasting up to six months in skin, and framed as a way to monitor UV exposure for skin cancer prevention. The new inks stay available for much longer: all three channels remained switchable in skin for 1.4 to 2.2 years, the report says, though it does not spell out how that range was measured.

From the lab to Magic Ink and a purple bottle

Commercial development runs through HYPRSKN, a biotech company that Bruns and former PhD student Jess Butterfield co-founded through CU Boulder’s Venture Partners office. Its product, Magic Ink, lets artists selectively turn parts of a tattoo on and off to change the design, according to the university’s April 2023 announcement of his $605,000 National Science Foundation CAREER Award. That award funds a library of nanoparticles varying in size, composition, surface chemistry, density and stiffness, which Bruns plans to test for immunogenicity, toxicity and migration in the body in the hope of establishing safety guidelines for ordinary and smart tattoos.

Live Science says third-party medical tests found the purple ink safe and that only purple is commercially available so far, at about $100 for a small bottle. Scripps News reported in September 2023 that Magic Ink had been tested on more than 50 people. Bruns pitched the use then: tattoos that can be hidden when visiting family or appearing in court, and a way for cancer patients to avoid permanent alignment marks for radiation. Carson Bruns, the lab’s principal investigator, has framed the reasoning before: ordinary tattoo pigments are essentially nanoparticles, the 2023 CU Boulder announcement notes, yet modern nanotechnology tools have barely been applied to tattooing. The unanswered detail in the new paper is the basis for the 1.4-to-2.2-year switchability range, which the coverage leaves unexplained.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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