PhotoTat: The Light-Activated Tattoo Ink That Can Change or Disappear

Researchers have developed a new type of tattoo ink that can be switched on and off with light. Called PhotoTat, the technology allows colors and images embedded in the skin to appear, change or fade without going through the painful tattoo-removal process.

The light-activated tattoo ink could eventually give people a way to hide or change permanent body art. It may also have medical applications, including tattoos that appear only when a doctor needs to see them. The research was reported in a study published in Matter & Light.

“This is a tattoo you can get, and if you don’t want it to be visible anymore or just don’t want it, you can just turn it off,” study co-author Carson Bruns, an associate professor of biomedical engineering at the University of Colorado Boulder, said. “That’s it. You don’t need to turn it on again.”

How PhotoTat light-activated tattoo ink works

PhotoTat contains three primary-color inks: blue, magenta and yellow. Each ink uses a photochromic dye, a photosensitive compound that changes color when exposed to different wavelengths of light.

The dyes are encapsulated in nanoparticles made from polymethyl methacrylate, or PMMA. This medical-grade glassy plastic is already used in medical implants and dermal fillers.

When exposed to specific wavelengths of light, the dyes change their molecular structure. A 365-nanometer ultraviolet LED can activate the dye in about two to three seconds. Once activated, the color can remain visible for hours to days under normal indoor lighting.

Bright sunlight has the opposite effect. When the wearer exposes the tattoo to strong outdoor light, the color fades within seconds and becomes invisible. The pigment itself remains in the skin; only the tattoo’s appearance changes.

In tests, all three PhotoTat color channels could be switched within the skin for between 1.4 and 2.2 years.

One tattoo can display different colors and designs

Using three colors allows different parts of a tattoo to be activated with different wavelengths of light. For example, green light can illuminate the magenta portion of the design, while blue light can activate the yellow pigment.

This gives wearers the ability to customize a tattoo’s appearance. A design could show purple cherries at one point and groups of yellow hearts at another, depending on which colors are activated.

The feature could appeal to people who already have tattoos but want to add something playful without committing to another permanent design. Bruns tested the ink on his own skin, creating a series of tattooed scales with different ink formations.

“These scales are like lab vessels, so I purposely gave them to myself,” Bruns said, joking that the results looked like a “magical mermaid trick.” Some scales appeared from nowhere, while others changed color when activated.

Can PhotoTat tattoos be hidden?

PhotoTat can also be combined with conventional tattoo ink. A permanent black design, for example, could include a hidden PhotoTat element that appears only after it is activated with light.

The technology may be useful for people who want a tattoo but feel hesitant about its permanence. It could also help people temporarily cover tattoos because of work requirements, social expectations or family commitments.

“Most of the time it’s on, but just for this moment, for example, I turn it off for grandma,” Bruns said.

Potential medical uses for light-activated tattoos

Bruns believes PhotoTat could also be useful in medical settings. Patients receiving radiation therapy may receive permanent tattoos that help doctors aim radiation beams precisely.

Although these markings are useful during treatment, they remain after therapy and can remind patients of their experience. PhotoTat could make similar markings invisible when patients no longer need to see them.

The ink might also be used to display markings during surgery and hide them afterward. These applications remain potential uses of the technology rather than established medical treatments.

Bruns has spent several years developing other smart tattoos for medical purposes. These include dosimeter-type tattoos that measure the amount of ultraviolet radiation a wearer experiences.

Other smart tattoos under development can change color when a wearer is exposed to hazardous environments, including environments involving gamma rays.

“Not for you or me, but people like astronauts and nuclear engineers have to wear these dosimeters,” Bruns said. “So we have something like a dosimeter tattoo on our skin.”

When will PhotoTat ink be available?

Bruns and his fellow tattoo artists have begun the commercialization of purple PhotoTat ink after the ink passed a series of third-party medical tests.

Tests have shown that the purple ink is safe to use and can be ordered. However, it costs $100 for a small bottle. Bruns hopes continued research will bring additional colors to market, reduce production costs and make the light-activated tattoo technology more accessible.