There have been a growing number of reports suggesting that ear temperature measurement is unreliable and by implication so is the device. Examination of the measurement site, the tympanic membrane (eardrum) and the walls of the external auditory meatus (ear canal) reveals that at least some of the unreliability might derive from poor aiming of the infrared thermometer: the ear canal walls have a lower temperature than the eardrum. Additionally, anatomical properties of the ear canal may increase the difficulty of aiming the thermometer at the eardrum. Furthermore, the rich vascularization, innervation and variations in skin properties (thickness, oil secretion and hair) along the length of the ear canal affect the black body-like nature of the structure. It is concluded that such factors are more likely underlying reasons for the difficulties in reliably reproducing temperatures from this site. We conclude that concerns should extend beyond the reliability of the device and there should be greater study of the measurement site. The argument extends to all sites chosen for clinical assessment of the patient, as previous studies of the alternative temperature measurement sites are also unfortunately few and tend to be lacking in scientific rigour.