Color-Changing Tattoo Ink Works. Is It Safe? What the Studies Show
PhotoTat can make a tattoo visible or nearly invisible with light. It comes from Carson Bruns' lab at the University of Colorado Boulder, and the effect is impressive. As someone who formulates ink, I want to know what was tested beyond the color change.
What it is
PhotoTat is three primary-color aqueous inks made of PMMA nanoparticles, each doped with a diarylethene photochromic dye. UV and certain wavelengths of visible light switch the dyes on and off. The paper points to PMMA's use in approved permanent implants such as bone cement, intraocular lenses and dermal fillers.
The three-color inks were tested in silicone and pig skin models and on the lead author himself, who filled in a fish-scale outline on his leg. One secondary report says those tattoos stayed switchable for up to 2.2 years, a single person with no reported adverse events.
What has been shown
The human data comes from the earlier single-color Magic Ink, now sold commercially. The clinical study published July 2, 2026 tested that formulation. That distinction matters when reading the results.
11 participants each received a Magic Ink tattoo and a matched commercial control tattoo. No adverse events in either group, with no significant difference in pain, redness or itch. The preclinical work included third-party-verified sterility and non-cytotoxicity, and the tattoos still switched after at least a year in the skin.
Those results are encouraging for the formulation tested. They leave several questions about the three-color version.
What has not been shown
The authors say the trial validated a monochromatic formulation, while PhotoTat uses three photochromes at their own loadings. That leaves PhotoTat's three-color formula outside the clinical result.
The duration of the color effect also needs separating from the safety assessments. Healing was assessed by inspection at days 7 and 21, surveys through day 21, and photographs over five months. With eleven participants, this was a pilot clinical evaluation, not a population-scale study.
The ink was developed in the same lab that went on to commercialize it, so independent replication would be useful. Reporting says Bruns has not yet determined whether the inks are safe for people, and that PhotoTat still needs toxicity, sterility and purity testing.
Questions I still have about the formulation
The dyes change molecular structure each time they switch. The preclinical work reports high fatigue resistance, but that describes the color change. I have not found published data on what years of repeated switching do to the dye, the polymer shell, any breakdown products, or where the particles end up in tissue.
There is also a purity question. The preparation described in the paper dissolves the PMMA and dye in dichloromethane. I have not found residual-solvent data for a finished ink. I am raising it as a question, not a finding.
For what is known about ink particles in the body, see can tattoo ink reach the brain? and do tattoo ink ingredients interact?
What this means for artists
Before using an ink like this, I would ask for sterility and cytotoxicity results for the exact formulation in the bottle. I'd also want to know how many people were followed, for how long, and whether independent researchers have repeated the work. An ink that still changes color has demonstrated optical performance; its biological safety needs its own evidence.
Sources
The same clinical study, PubMed abstract
Phys.org: light-responsive inks could make tattoos visible on demand, but safety remains unproven
The Scientist: invisible ink could make tattoos less permanent
The Brighter Side of News: light-activated tattoo inks (source of the 2.2-year report)
This is my reading of the published work, with my own formulation questions above. The clinical study was available to me as an abstract, so I haven't assessed its full methods or disclosures. It isn't medical advice.
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