Tattoos have been considered permanent for decades: what is once applied to the skin usually stays with a person for life, and getting rid of it requires removal agents or a laser. A group of researchers from the University of Colorado Boulder has shown that this is not necessarily the case. In a recent publication in the journal Matter & Light, scientists described a method where photochromic dyes encased in tiny plexiglass spheres act as the pigment. Under ultraviolet light, such a design appears, and under normal visible light, it disappears—meaning a tattoo can literally be 'switched off' and 'switched on' with light.
How Phototat Technology Works
The authors named the method Phototat. It is based on three primary dyes: magenta, yellow, and blue. By mixing them in various proportions, almost any shade can be achieved, making it a full-color tattoo rather than a monochrome sketch. The pigment itself is packaged in nanosized spheres that are retained in the dermis and ensure the stability of the design over a long period. According to the developers, photochromic dyes transition from a transparent state to a colored state when exposed to light of a specific wavelength.
From Lab to Skin: Twelve Months on His Own Leg
Nanoscientist Carson Bruns, one of the developers, did not limit himself to laboratory test tubes: testing the ink on his own skin has become 'almost a tradition' within his team, he says. For twelve months, he applied three dyes and their mixtures to his own leg, creating new colors. The resulting tattoos lasted for over two years, which is a significant period for an experimental pigment. According to New Scientist, Bruns already has a fish-scale design on his skin applied using this technique, and he has noted no known side effects: 'Although it has been on my skin for over two years now, I haven't noticed any obvious fading.'
Background: 'Solar Freckles' as an Indicator
Previously, Bruns had already experimented with color-changing ink. He applied so-called 'solar freckles' to himself—a pattern that darkens and turns bluer as UV levels rise. This approach allowed for visually tracking how much time the skin spent in the sun, turning the tattoo into a kind of indicator. The new Phototat method logically continues this line, but in the format of a full-color image rather than a simple marker.
Medicine Today, Tattoo Culture Tomorrow
Initially, the work is oriented toward medical scenarios—situations where it is important to temporarily mark the skin rather than leave a permanent trace. The technology is not yet ready for a wide audience: before Phototat becomes available, tests on other people, not just the author himself, are necessary. This is a standard but mandatory stage, without which no new pigment will leave the laboratory. However, the very fact that a tattoo can be made 'switchable' changes the perception of what it means to be tattooed: the industry has spent years moving toward increasingly complex machines and pigments, but reversibility remained on the periphery, and here it is embedded directly into the chemistry of the ink. Perhaps in a few years, the market will see inks that allow wearing a design according to mood or necessity rather than for life—ranging from temporary markers to interactive patterns that react to light.
