Effects of cellular phone use on ear canal temperature measured by NTC thermistors

Summary The earlier studies using phantom models and human subjects concerning warming effects during cellular phone use have been controversial, partly because radiofrequency (RF) exposures have been variable. In this randomized, double‐blind, placebo‐controlled crossover trial, 30 healthy subjects were submitted to 900 MHz (2W) and 1800 MHz (1W) cellular phone RF exposure, and to sham exposure in separate study sessions. Temperature signals were recorded continuously in both ear canals before, during and after the 35‐min RF exposure and the 35‐min sham exposure sessions. Temperature was measured by using small‐sized NTC thermistors placed in the ear canals through disposable ear plugs. The mean temperature changes were determined during a set cardiovascular autonomic function studies: during a 5‐min controlled breathing test, during a 5‐min spontaneous breathing test, during 7‐min head‐up tilting, 1‐min before, during and after two consecutive Valsalva manoeuvres and during a deep breathing test. Temperatures in the exposed ear were significantly higher during RF exposures compared with sham exposure in both 900 and 1800 MHz studies with maximum differences of 1·2 ± 0·5°C (900 MHz exposure) and 1·3 ± 0·7°C (1800 MHz exposure). Temperatures in the RF‐exposed ear were also significantly higher during the postexposure period compared with post‐sham exposure period with maximum differences of 0·6 ± 0·3°C for 900 MHz and 0·5 ± 0·5°C for 1800 MHz. The results of this study suggest that RF exposure to a cellular phone, either using 900 or 1800 MHz with their maximal allowed antenna powers, increases the temperature in the ear canal. The reason for the ear canal temperature rising is a consequence of mobile phone battery warming during maximal antenna power use. The earlier published articles do not indicate that temperature rising in the ear canal has any significant contribution from the RF fields emitted from mobile phones.