PhotoTat: UV-switchable tattoo ink uses photochromic dyes encapsulated in PMMA for invisible-to-visible color changes

This explainer summarises content from The Conversation about PhotoTat, an invisible tattoo ink system that uses photochromic dyes encapsulated in PMMA to switch colors under UV light and turn color off with white light. The article discusses how the pigments change structure to produce color, the stability and cycle life of the dyes, and plans for additional colors and integration with conventional tattoo inks. It also covers potential medical uses and the regulatory and safety challenges ahead.

• PhotoTat inks are PMMA-encapsulated photochromic dyes that reveal colour under UV light and revert under white light.
• Blue pigments degrade after 10–100 activations, while newer dyes promise 10,000 activation cycles with months-long colour stability.
• A palette including blue, magenta, and yellow supports 16 colours when mixed with conventional tattoo ink.
• Market timing faces safety testing, regulatory review, sunscreen UV protection, and indoor light resetting the colour over days.

Overview

The Conversation reports on a novel approach to switchable tattoo ink developed by Carson Bruns and colleagues at the University of Colorado Boulder. The team created PhotoTat inks by encapsulating photochromic dyes in poly(methyl methacrylate) PMMA. This approach yields inks that stay colourless until exposed to bright ultraviolet (UV) light, which activates a chemical ring-closure in the dye to produce a coloured pigment. A blast of bright white light reverses the reaction, turning the colour off again. This dynamic enables tattoos to be invisible for everyday life and revealed for events or medical procedures as needed. The researchers demonstrated several motifs, including a lantern that lights up when activated and multicoloured scales reminiscent of The Rainbow Fish. The pigments are photochromic dyes, a class known to change colour in response to light, a concept familiar from photochromic sunglasses.

The research, published in Matter & Light, describes how encapsulation in PMMA both stabilises the colour and makes it compatible with tattoo media. The ink family, termed PhotoTat, can be combined with conventional tattoo inks to colourise elements that activate under UV light and decolourise under white light. This combination approach broadens the palette beyond a single dye, enabling a range of colours by adjusting the dye structure and pigment formulation.

How PhotoTat works

Photochromic dyes switch between two forms in response to light. In PhotoTat, brief exposure (two to three seconds) to bright UV light forms a new ring within the dye molecule, converting a colourless pigment to a coloured form. The colour depends on the exact molecular structure, with various hues available by design. A subsequent exposure to white light breaks the ring, restoring the colourless form. This reversible, light-driven process is the core mechanism enabling switchable tattoos.

For a long time, the challenge with photochromic pigments was instability: at higher temperatures the coloured form would revert to colourless and the dyes could fatigue after numerous activation cycles, leading to permanent colouration. Recent dye design strategies have produced markedly stable dyes, capable of more than 10,000 on-off cycles without degradation and colour retention for months, a critical milestone for practical use in tattoo inks.

Bruns’ team encapsulated the photochromic pigments in PMMA, a polymer already approved for medical use in bone cement and intraocular lenses, which helps ensure biocompatibility and printability for tattoo applications. This PhotoTat PMMA encapsulation is what makes the pigment compatible with conventional tattoo formulations while preserving the light-responsive behavior.

Ink palette and colours

The researchers introduced several PhotoTat motifs, including a blue ink and other hues that can be tuned. They also demonstrated a magenta and a yellow PhotoTat pigment, which can be combined to produce up to 16 colours when used together with standard tattoo inks. The palette expands through molecular design of the photochromic dyes, enabling a broader range of colour shifts than a single dye would provide. The team notes that one pigment (blue) currently degrades after 10–100 activations, potentially leaving a permanent purple mark, which points to the need for continued dye improvement for robust clinical and consumer use.

Market context and time to market

In 2024, a red photochromic pigment branded as Magic Ink was launched by Hyprskn, a Colorado-based biotech company. A 2 millilitre vial is priced at about £77, a premium reflecting the specialised dyes and formulation steps required. The product is reported to comply with the EU Reach regulations, signaling regulatory alignment in at least one major market. Bruns and colleagues have since developed three additional PhotoTat inks—blue, magenta and yellow—that can mix into 16 combinations when paired with conventional tattoo inks. Bruns has tested the inks extensively on his own body, reporting positive results, but broader testing and peer-reviewed safety assessments remain essential for commercial roll-out.

Safety and toxicity testing

Despite the promise, several safety concerns must be addressed before PhotoTat inks can be used in tattoo shops. Photochromic dyes historically have had issues with stability and potential pigment leakage from encapsulation media. The article notes that the blue ink currently degrades after 10–100 activations, potentially producing a lasting pigment change. Indoor lighting can cause gradual deactivation over days, while direct sunlight generates UV exposure that can activate the inks unless sunscreen is used. Confirmation of long-term safety will require thorough toxicology and biocompatibility testing, as well as dermatological and ocular safety assessments given potential exposure routes.

Applications and ethical considerations

Beyond aesthetic, switchable tattoos could have meaningful clinical applications. Bruns imagines use in guiding radiation therapy or identifying biopsy sites where tattoo marks might otherwise be permanent and distressing for patients. The ability to render marks invisible after clinical use could mitigate trauma associated with enduring skin markings. Nevertheless, researchers must balance attractive features with safety, regulatory compliance and the ethical implications of medical pigment use in patients’ skin and potential cross-use in cosmetics and fashion.

Industry reception and challenges ahead

The reception to Magic Ink has been mixed within the tattoo community, with some embracing new creative tools and others viewing it as a premium, possibly gimmicky product. Bruns frames PhotoTat as both a creative medium and a potential medical aid, emphasising patient welfare and the ability to control when and how markings appear. Major challenges include ensuring consistent colour stability across individuals and environments, validating toxicity and safety in line with medical device or cosmetic regulations, and navigating sunscreen performance and indoor lighting effects in real-world settings. The scale-up from laboratory demonstration to shop-floor availability will require extensive testing, regulatory clearance, and consumer education about safety and usage limits.

Conclusion

The PhotoTat project represents a convergence of chemistry, materials science and medical thinking to deliver switchable, UV-activated tattoo inks. The PMMA-encapsulated photochromic dyes offer a path to colours that appear on demand and fade with white light, with the potential to transform tattoo art and certain clinical workflows. However, achieving widespread adoption will hinge on overcoming dye stability issues, confirming long-term safety, and aligning with stringent regulatory standards. If these hurdles can be cleared, PhotoTat could enable tattoos that adapt to contexts such as professional requirements or medical needs, while still offering creative expression for wearers.