This paper reports a novel fully integrated low power multi-sensing smart system, which, by wafer-level 3D heterogeneous integration of Ion Sensitive Fully Depleted (FD) FETs and SU-8 micro/nanofludics, achieves the first of its kind wearable multi-sensing system, called Lab on Skin TM , capable to detect biomarkers in human sweat. In the reported configuration, the multi-sensing system exploits arrays of functionalized sensors capable to simultaneously detect pH, Na+ and K+ concentrations in sweat in real time. We present a detailed electrical DC and dynamic characterization, showing excellent sensitivities (52mV/dec for pH and -37mV/dec for Na + sensors) with ultra-low power consumption (less than 50 nWatts/sensor). We report ion cross-sensitivities and a differential measurement approach that allows calibrated measurements. Overall, the paper reports significant advances in the design and fabrication of micro/nanofludics channels, inlets compatible with human skin pore size and density, and outlet passive pumps with flow rates of tens of pl/s; all capable of exploiting capillary forces in order to provide a zero energy pumping of sweat into sensing channels. Moreover, we report the first integration of a miniaturized Ag/AgCl Quasi-Reference Electrodes (QRE) into the sensing system, with long term stability, paving the way for fully wearable electronic chips in flexible patches or as plug-in modules in wrist based devices.