Wearable system based on an in-situ four-probe impedance measurement at different signal frequencies for the topical monitoring of at least one physiological parameter reflecting the hydration status such as skin conductivity, ion concentration in sweat or red blood cell characteristics. The said system is comprising a flexible substrate adapted to be directly or indirectly fixed to the skin and a plurality of conductive electrodes designed to be in contact with the body and to enable a four-probe measurements of the bio-impedance of tissue and/or skin at one or more tissue site. One embodiment includes at least a temperature sensor serving both the calibration of the impedance measurements as well as for the estimation of the temperature effect on hydration status, allowing the fine-tuning of the hydration status evaluation.