A non-invasive method of measuring the temperature of a subject through a portable infrared thermometer includes measuring a temperature related to room temperature and detecting an infrared radiation coming from a region of interest of the subject. The region of interest can be a forehead or an auricle area of the subject. The portable infrared thermometer detecting the infrared radiation determines a surface temperature of the region of interest. A corrective parameter is determined based on the temperature related to the room temperature, and the surface temperature measured by the portable infrared thermometer on the surface portion of the forehead or of the auricle area is corrected using the corrective parameter. The real inner temperature of the subject is determined based upon the correcting.