There's a common problem with health-tracking devices like smartwatches: they're not really attached to you, which leaves you relying on a short-lived battery and a wireless connection. Even a self-powered patch has its limits. That's where Harvard and MIT think they can help: they've developed smart tattoos that effectively place health sensors in your skin, no power or wireless link required. The ink in the tattoos reacts to the chemical composition of your interstitial fluid, which reflects the state of your blood. A green ink grows more intense to let athletes know when they're dehydrated, while another green ink turns brown to warn diabetics when their glucose levels go up.
And unlike that tattoo you got on a wild night in college, you're not stuck with it. With enough refinement, the scientists expect to make tattoos that only last for as long as you need them. They could be invisible unless subjected to certain kinds of light, too, so you wouldn't have to explain your ink to your friends. if you weren't sure what the symbols on your arm meant, a smartphone app could analyze them to tell you exactly how you're doing.
It could be a long while before you're sporting tattoos that are as informative as they are decorative. The project is as much about inspiring "potential" among both artists and scientists, as well as to address ethical questions. If your tattoo is visible, are you comfortable with the idea of everyone seeing your blood sugar level the moment you put on a short-sleeved shirt? Look at it this way, though: if you're tired of strapping devices to your arms or wrists just to quantify your health, this could be much more comfortable.