International audienceMobile phone "cell phone" use has dramatically increased over th last decade, but doubts remain over its safety. Epidemiological investigation of mobile phone (MP) users reported symptoms of discomfort feeling, warmth behind/around or on the ear and heat sensation of the cheek. These symptoms may be due to thermal insulation, conduction of the heat produced in the phone by the battery currents and running of the radiofrequency (RF) electronic circuits, and electromagnetic field (EMF) energy absorbed by the user's head. Using a Luxtron 790 fiberoptic thermometer we measured the temperature of the temporal skin due to GSM 1800 MHz MP radiated power (125 mW). To perform a sham exposure, we suppressed the EMF exposure by switching the RF signal from the antenna to a 50 Ohms load. The ambient air temperature was 23°C, the relative humidity was 50 +- 10 %, the air flow rate in the room was 0.01 m.s-1 (natural convection) and the MP was held in the normal position of use "cheek position" (CENELEC Standard 50361) for 30 minutes to reach the thermal steady state. With a switched off MP, the increase in skin temperature was statistically significant 1.88°C. When MP was switched on, the increase was 2.93°C in reception mode, 3.29°C in emission mode without load and 3.31 °C in emission mode with load. The temperature difference with or without load was not significant (t = 0.707; p = 0.489), which means that the contribution of EMF absorption to skin heating is negligible. The highest temperature increases detected during these experiments (TSkin = 37.1°C ~ core temperature) are in the environmental range and are lower than those physiologically experienced by the surface skin during hot summer days. No skin damage by thermal insuit is experienced for Tskin < 44°C, whereby a pain sensation replaces the feeling of temperature elevation in humans. This local skin temperature increase will cause thermoregulation responses. The skin blood vessels will be dilated and skin will be wet. The result suggests that the heat sensations reported by the MP users are exclusively caused by thermal insulation and heat conduction from MP associated with long calling time. No thermal skin damage can be suspected using MP in normal use