Light-activated tattoo ink can be turned on and off — SkimNews
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- Carson Bruns at the University of Colorado led the development of 'PhotoTat' — tattoo inks using photochromic dyes that switch from transparent to colored under UV light and back to clear under bright visible light, allowing wearers to turn tattoos on and off at will.
- Bruns has worn a fish-scale PhotoTat tattoo on himself for over two years, reporting no obvious fading; the technology has also been tested on silicon.
- The pigments are delivered through the same needle-into-dermis method as traditional tattoos with the same machines, meaning the tattoo is permanent even as its appearance cyclically changes.
- The technology currently comes in 16 clearly distinguishable colors producing at least 300 shades, though white is impossible (reflects rather than absorbs light) and a true cyan has not been achieved.
- Known flaws include the blue ink slowly developing a permanent purplish tint through photo-degradation over many on/off cycles, and wearers needing sunscreen to prevent sunlight from unintentionally triggering the color.
- Signe Bedsted Clemmensen at the University of Southern Denmark cautioned that tattoo ink remains a foreign substance linked to cancer regardless of whether it is visible, and extensive safety studies — including toxicity of the color-switching dye — must precede public release.
- Findings were published in Matter & Light (DOI: 10.1016/j.matlit.2026.100119); a proposed medical application is temporary markers radiologists use to guide radiation beams, sparing patients from permanent skin markings.
Why it matters: If adopted, PhotoTat could spare radiation-therapy patients from the permanent skin markings radiologists currently rely on to aim their beams, while giving ordinary wearers on-demand control over visible ink. But the blue dye's slow photo-degradation into permanent purple and the still-unknown toxicity of the color-switching pigments mean safety trials must clear before any commercial rollout becomes viable.
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