What if you could track your blood sugar, check if you're dehydrated, or be alerted to a potential health issue just by looking at your skin? Enter smart tattoos – a form of biotechnology that uses nanosensors embedded in the skin to monitor your health in real time.
They're designed to interact with fluctuations in your body's chemistry. By detecting changes in interstitial fluid – fluid found in the space between cells – the ink can tell the wearer about measurable things such as glucose, pH, or electrolyte levels by changing color.
For people with chronic conditions like diabetes, this could mean managing their health without daily finger pricks or bulky monitoring devices. But there are a few hurdles researchers must overcome before smart tattoos become available to the public.
What Makes a Tattoo Smart?
At a glance, you can't tell smart tattoos from regular, everyday tattoos. They are applied the same way, too: with a sterile needle and ink. The specialized ink reacts with physiological markers on or under the skin, changing color in response to changes in metrics such as glucose, sodium, or hydration levels.
Ali K. Yetisen, a researcher and associate professor at Imperial College London, has worked in smart tattoo development for much of his career. He studies smart tattoos that measure interstitial fluid in the body, which can act as a substitute for blood in tracking health metrics.
He began his research at Harvard Medical School with a team of researchers from both Harvard and the Massachusetts Institute of Technology. They created four tattoos to track three metrics: a pH sensor that changed from purple to pink, a glucose sensor that changed from blue to brown, and a sodium and pH sensor that became brighter under ultraviolet (UV) light.
Yetisen said the goal for these tattoos was not only to measure one specific metric, but also to be able to take multiple measurements at once in real time. And soon, he hopes this technology will expand not only to measure physical metrics, but to neuropsychiatric ones as well, such as serotonin and dopamine.
One of the challenges that could be keeping the technology from advancing is that most sensors can work only once. This means that after they change color once, they can't be used again.
Yetisen said this phenomenon – which he called reversibility – is one of the biggest hurdles in bringing smart tattoos to the market. It is also an issue that he is still working to overcome today.
Ideally, he said, the tattoos will be able to be read using the camera on a smartphone. The phone camera would analyze a wearable device that sits on the skin and captures data in real time.
"The idea is that these sensors will serve as a companion diagnostic device," Yetisen said. "For example, that means that if somebody is taking a medication, they will be able to monitor the concentrations of some of these drugs or biomarkers in real time."
Magic Ink: Smart Tattoos That Only Appear When Needed
The challenges that come with smart tattoos measuring interstitial fluid motivated Carson Bruns, an assistant professor of mechanical engineering at the University of Colorado Boulder, to look for a different method. He decided to focus on tattoos that measure elements outside of the skin instead of under it.
The first tattoo he and his team developed was called a solar freckle: a tiny dot on the skin that can sense ultraviolet rays. It's completely invisible while indoors or in the shade, but when skin is exposed to ultraviolet rays, it turns blue. After sunscreen is applied or a patient is out of the sun, the dot disappears.
The technology, dubbed Magic Ink, can also be used for people who are getting radiation treatment for cancer. Currently, patients are marked with tattoos that look like small dots to help doctors target the correct area during radiation treatment. Because these tattoos are permanent, Bruns said they often serve as a negative reminder to patients of their time getting cancer treatment.
"We think Magic Ink is perfect [for those patients]," he said. "This is a tattoo that only has to be visible when you go to the doctor, and it can be invisible the rest of the time."
Aesthetically, Bruns said, a smart tattoo can take any form. Not only can it look like a regular tattoo, but it can also be put into a tattoo a customer already has, meaning only one part of the tattoo would be inked with Magic Ink. Another option is to get a standalone nanotattoo in the design of the customer's choice.
In both options, the smart tattoo appears only when exposed to its trigger – for example, UV light.
Bruns said in terms of longevity, the ink has come a long way. While earlier versions of it would disappear after six to eight months, the new ink – made out of biomedical-grade polymer glass used in some other biomedical implants – is made to last a lifetime.
So far, he knows the ink can last at least three years, because that's how long they've lasted on his own skin.
"Every color-changing ink that we make, I pretty much tattoo on myself," Bruns said. "So I have, like, hundreds of these tattoos on my body."
Magic Ink is currently available to the public.
Temporary Smart Tattoos: A Happy Medium?
For those who may not feel comfortable enough to use permanent ink but still want to try out the technology, there is an alternative: temporary tattoos. After the technology hit the shelves, other players have entered the market, albeit with a very different approach.
LogicInk is one of those players. Backed by large venture capital firms such as Village Global and West Ventures, the company offers temporary tattoos that measure sun exposure via ultraviolet rays and hydration via electrolytes. The company's website says there are also new versions of its tattoos in development that will measure how likely it is to get genetic conditions and screen for concussions.
While these tattoos can offer a viable alternative to permanent ink, they may come with the same drawbacks as other wearable medical technology, including the need for reapplication and issues with accuracy as people sweat, rub their skin, or come into contact with water.
Overcoming Stigma and Bringing Smart Tattoos to the Public
Bruns shared details about his early research in a 2018 TED Talk, which he said caught the attention of Keith "Bang Bang" McCurdy, a celebrity tattoo artist who has inked A-listers such as Rihanna, Selena Gomez, and Miley Cyrus. Bruns said after inviting McCurdy to his lab to see the technology for himself, the pair co-founded a company called HYPRSKN focused on bringing products to market.
Magic Ink is a subsidiary of HYPRSKN, and according to the company's website, it is the world's first rewritable, erasable, reprogrammable smart tattoo ink.
Today, Bruns and his team are working on a new kind of tattoo that builds on these findings. Instead of sensing sunscreen on the skin, Bruns said, the tattoo would act as a permanent sunscreen – a barrier on top of the skin that would protect from ultraviolet rays for the rest of a person’s life.
These permanent sunscreen tattoos are being tested in mice. Bruns said HYPRSKN owns the intellectual property and plans to commercialize the product as soon as it proves safe and effective in humans.
As time goes on and wearable technology such as smart watches and continuous glucose monitors become more popular, some researchers, including the authors of a recent review of the technology, believe smart tattoos "present a promising avenue in wearable healthcare technology."
Still, many consumers may be wary of a permanent medical device implanted in the skin. Others may be hesitant about tattoos in general, as they still have a stigma in many cultures. But the extent of that stigma remains unclear.
For example, one 2018 study found that having a tattoo does not appear to be linked to disadvantage or discrimination in the labor market. A similar study published in 2022 found that applicants with tattoos were less likely to be hired, especially if the tattoos were visible.
Even so, Yetisen is optimistic about the future of smart tattoos. He said he expects smart tattoos that can measure multiple things about the body to be available to consumers in just five to 10 years.
