That’s what new smart inks developed to detect dehydration or blood sugar levels could provide. Researchers from Harvard and MIT have developed two inks that change color depending on body chemistry. One turns from green to brown as glucose levels rise, while another gets more green (sadly only under blue light) in the presence of increasing sodium concentration (which is a proxy for dehydration). The team, which presented its research at the International Symposium on Wearable Computers earlier this month, has shown that tattoos drawn on pig skin using the inks work as they describe. It also suggests that in the future the tattoos could be used to provide wearable displays on human skin.