RF exposure during MR exams induces heating of the exposed tissues. Measurement of tympanic membrane temperature with an infrared sensor has been used to estimate non-invasively the global RF-induced temperature rise. In this study, the tympanic membrane temperature was measured before and after having the volunteers lying for 15 minutes with earplugs with neither an RF nor a static magnetic field. Large physiological variations of temperature rise were observed across the volunteers after this dummy “exposure”, showing the low reliability of this metric to measure small temperature rises, that make it problematic for RF-induced temperature rise estimation.