Originally published 2019-09-04.
Colour-changing tattoo sensors are tattoo inks that react to chemicals in the fluid under the skin, so the colour of the design shows whether a health marker is high or low. In 2019 a team at the Technical University of Munich (TUM) showed inks that change colour with three markers: pH, glucose and albumin. The idea is that people with diabetes or kidney disease could one day check a tattoo, or photograph it with a phone, instead of giving repeated blood samples.
The important caveat comes first: these sensors were tested only in patches of pig skin, not in people. They are a promising laboratory concept, not a product you can get at a tattoo studio or use to manage a medical condition.
Who developed the sensors
The research was led by Ali K. Yetisen at TUM and published in July 2019 in the chemistry journal Angewandte Chemie International Edition under the title “Dermal Tattoo Biosensors for Colorimetric Metabolite Detection.” The journal’s publisher highlighted the work in its press materials.
The team’s starting point was simple. Many medical tests need blood drawn, sent to a lab and analysed, which takes time. A sensor placed in the skin itself could, in principle, show changes on the spot, with no delay and possibly over a long period. Tattooing is an ancient, well-understood way of placing pigment permanently in the dermis, the layer of skin below the surface, so the researchers asked whether that pigment could be swapped for something that reacts chemically.
How each colour-changing ink works
Instead of ordinary pigment, the researchers injected small amounts of sensor solution into the skin. Each formulation was designed to respond to one marker in the interstitial fluid, the liquid that surrounds cells and reflects what is happening in the blood.
pH sensor
A mix of three classic indicator dyes, methyl red, bromothymol blue and phenolphthalein, shifts from yellow to blue as pH rises from 5 to 9. pH describes how acidic or alkaline a fluid is, and the body keeps it within a narrow range, so a change can signal metabolic problems.
Glucose sensor
This one relies on two enzymes, glucose oxidase and peroxidase. When glucose is present, their reactions alter the structure of an organic pigment, turning it from yellow towards dark green. Higher glucose gives a stronger change, which is the signal that matters for diabetes.
Albumin sensor
Albumin is the most common protein in blood plasma. It carries hormones, drugs and other substances and helps keep fluid inside blood vessels. Here a yellow dye turns green when it binds to albumin. Low albumin can be linked to liver or kidney disease, which is why the team chose it.
Mikhail_Kayl/Shutterstock
How the inks were tested
The team tattooed several sensor patches into pieces of pig skin, a material tattoo artists often use for practice because it behaves much like human skin. They then changed the levels of glucose, albumin or pH in the surrounding fluid and watched the colours shift.
Rather than relying on the human eye, which can misjudge colour in different lighting, they measured the result with an ordinary smartphone camera and an app. This matters: a future version would probably depend on a phone to turn a colour into a number.
Contemporary coverage reported a key limitation. Only the pH sensor could change back and forth repeatedly, while the glucose and albumin sensors reportedly changed only once. A sensor that can only react once is not useful for long-term monitoring, so the researchers said they hoped to make all the inks reversible, for example by using synthetic receptors.
Earlier work: MIT and Harvard’s DermalAbyss
The Munich study was not the first of its kind. In 2017 researchers at the MIT Media Lab and Harvard Medical School presented DermalAbyss, a similar concept. According to a Snopes fact-check, its inks responded to glucose (blue to brown) and pH (pink to purple), and other versions glowed differently under ultraviolet light depending on sodium and pH levels. Earlier summaries that described the MIT inks as only glowing with pH and sodium left out the glucose sensor.
DermalAbyss was also tested only on pig skin. Its creators described it as a proof of concept and said they had no plans to develop it as a product or run clinical trials. That did not stop a 2017 social media meme from presenting it as a ready-made diabetes tattoo, shared hundreds of thousands of times.
Common myths about health-monitoring tattoos
- “You can already get one.” No colour-changing medical tattoo was approved for use in people when these studies were published.
- “It will replace glucose meters.” Possibly one day, but a sensor needs proven accuracy, stability over months or years, and clear calibration before it can guide treatment.
- “Any tattoo artist could do it.” The inks are laboratory chemicals. Their long-term safety inside living skin, and how the body would react to them, has not been established.
- “A colour is a diagnosis.” A colour change can suggest that something is different, but interpreting it needs lighting control, comparison standards and medical judgement.
What would need to happen next
For these sensors to become medical devices, researchers would need to show that the colours remain accurate and stable for a long time, that they respond quickly enough to be useful, and that the chemicals are safe to leave permanently in the body. Then would come trials in people and regulatory approval.
The TUM team said further studies would test whether tattoo artwork is suitable for diagnosis. They suggested that, with suitable sensors, the approach could also detect electrolytes, pathogens or dehydration. In the meantime, wearable devices such as continuous glucose monitors already let many people with diabetes track their levels without constant finger pricks.
If you live with diabetes or kidney disease, talk to a doctor about the monitoring options that are available now. Colour-changing tattoos are an interesting glimpse of where medicine might go, and a good example of how chemistry and body art can meet.
Sources: Analytica World, 22 July 2019: The art of sensing within the skin (TUM); Angewandte Chemie press release (Wiley); Snopes: diabetes tattoo fact-check (DermalAbyss); photo: Mikhail_Kayl/Shutterstock.
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