A tattoo could soon change color or become almost invisible simply by exposing it to the right kind of light.
Conventional tattoos are designed to remain visible for years. To alter a design, you generally have to add ink or try to remove it with a laser. Researchers at the University of Colorado have developed another approach: pigments that change color without leaving the skin.
Their ink, called PhotoTat, contains dyes enclosed in tiny plastic particles. These dyes have a special property: their appearance changes depending on the light they receive. Ultraviolet light makes the color appear, while sufficiently strong visible light can make it disappear.
The researchers prepared three basic colors: blue, yellow, and magenta, a pink with a hint of purple. By mixing them, they can obtain different shades. It even becomes possible to erase some colors without affecting the others by choosing the light used.
The team first created designs on materials that mimic skin. By illuminating certain areas with a small laser projector, they made multicolored patterns appear and then modified them. A few seconds of intense light were enough to change the appearance of the pigments.
One important difference should be emphasized: the design does not actually disappear from the skin. The ink particles remain implanted beneath the surface, even when the tattoo appears erased. The pattern can therefore be brought back without using a needle again.
One of the researchers even tested colors on a tattoo on his own leg, made up of scale-shaped patterns. But these are still limited experiments, not a safety validation for the general public. The new multicolored inks must in particular undergo more extensive toxicological studies.
Natural light could also alter the colors unintentionally. And some pigments, especially blue, gradually lose their ability to change appearance after many cycles. The researchers will have to correct these flaws before considering a widely used product.
Beyond decorative tattoos, this technique could be useful in medicine. Some patients undergoing radiotherapy receive small permanent marks that help position the equipment correctly. Inks made visible only during treatment could eliminate the need to keep these reference points visible afterward.