A core body temperature monitoring apparatus placed superdermally over a user's skin, comprising: a first temperature sensor positioned in proximity to the skin a second temperature sensor; a thermal insulation layer positioned intermediate the first and second temperature sensors and having a thermal conductivity constant; the first temperature sensor being configured for detecting the temperature in proximity to the skin, and the second temperature sensor being configured for detecting the temperature above the thermal insulation layer; a heater for heating the apparatus and a subdermal tissue region underlying the user's skin, said subdermal tissue region configured with at least one variable thermal tissue parameter; and characterised by a controller comprising a switch, the switch configured for alternating between a calibration mode, and a measurement mode; wherein in the calibration mode the controller is configured: to activate the heater for generating an isothermal channel so that the temperature measured by the first temperature sensor equals the temperature measured by the second temperature sensor and to determine an instantaneous calibration subdermal temperature, to deactivate the heater for creating a heat flow channel intermediate the first temperature sensor and the second temperature sensor, and to calculate the variable thermal tissue parameter based on the calculated instantaneous calibration subdermal temperature and the detected temperature measured by the first temperature sensor and by the second temperature sensor; and wherein in the measurement mode, wherein the heater is inactive, the controller is configured to determine the core body temperature based on the variable thermal tissue parameter, the thermal conductivity constant and detected temperatures, measured by the first temperature sensor and by the second temperature sensor. a first temperature sensor positioned in proximity to the skin a second temperature sensor; a thermal insulation layer positioned intermediate the first and second temperature sensors and having a thermal conductivity constant; the first temperature sensor being configured for detecting the temperature in proximity to the skin, and the second temperature sensor being configured for detecting the temperature above the thermal insulation layer; a heater for heating the apparatus and a subdermal tissue region underlying the user's skin, said subdermal tissue region configured with at least one variable thermal tissue parameter; and characterised by a controller comprising a switch, the switch configured for alternating between a calibration mode, and a measurement mode; wherein in the calibration mode the controller is configured: to activate the heater for generating an isothermal channel so that the temperature measured by the first temperature sensor equals the temperature measured by the second temperature sensor and to determine an instantaneous calibration subdermal temperature, to deactivate the heater for creating a heat flow channel intermediate the first temperature sensor and the second temperature sensor, and to calculate the variable thermal tissue parameter based on the calculated instantaneous calibration subdermal temperature and the detected temperature measured by the first temperature sensor and by the second temperature sensor; and to activate the heater for generating an isothermal channel so that the temperature measured by the first temperature sensor equals the temperature measured by the second temperature sensor and to determine an instantaneous calibration subdermal temperature, to deactivate the heater for creating a heat flow channel intermediate the first temperature sensor and the second temperature sensor, and to calculate the variable thermal tissue parameter based on the calculated instantaneous calibration subdermal temperature and the detected temperature measured by the first temperature sensor and by the second temperature sensor; and wherein in the measurement mode, wherein the heater is inactive, the controller is configured to determine the core body temperature based on the variable thermal tissue parameter, the thermal conductivity constant and detected temperatures, measured by the first temperature sensor and by the second temperature sensor.