Heavy metals such as lead and cadmium are present in batteries, cosmetics, food and other things that are part of everyday life. They are toxic when they accumulate in the human organism, potentially causing several health problems, but detecting them in body fluids requires expensive equipment and a controlled laboratory environment. Researchers at the University of São Paulo (USP) in Brazil have now developed a portable sensor made of simple materials to detect heavy metals in sweat, which is easily sampled.