From life-like faces to elaborate nature scenes, tattoos are a true art form. Although people have decorated their bodies for millennia for ceremonial and religious reasons, many people today adorn themselves with these images as a form of self-expression. But the inks used for tattoos are unregulated in the U.S., resulting in products whose components are largely a mystery. Now, researchers have analyzed almost 100 inks and report that even when these products include an ingredient label, the lists often aren't accurate. The team also detected small particles that could be harmful to cells.