The purpose of this study was to determine whether the cellular components of Hairless-rat skin are affected by a chronic local exposure to non-ionizing radiations of Global Mobile Phone System: GSM-900 or -1800 radiations at specific absorption rate (SAR) 2.5 and 5 W/kg.
Materials and methods: A selected part of the right back of five-week old female hairless rats was exposed or sham exposed
(n¼8) for 2 h per day, 5 days a week, for 12 weeks to GSM-900 or -1800 signals using a loop-antenna. At the end of the experiment, skin biopsies were taken.
Results: Analyses of skin sections using hematoxylin eosin saffron (HES) coloration showed no significant difference in skin
thickness among the groups. Immunohistochemical analysis of basal lamella cells in radiofrequency radiation (RFR)-
exposed epidermis showed that the ratio of the antigen Ki-67 (cellular proliferation marker) positive cells to total lamella cells
remained within the range of the normal proliferation ratio. No significant differences in the level of filaggrin, collagen, and
elastin were observed among the different groups.

Following the work described in the companion paper, we have investigated the effects of chronic exposure to mobile phone signals on the skin. We had already performed a 4-week sub-chronic preliminary study (unpublished results), which did not demonstrate any major physical and histological variations (as measured 72 h after the last exposure) in the skin of hairless rats exposed to GSM-900 at three specific absorption rate (SAR) levels. However, this work called for an extension of these biological measurements during a whole
skin-cell regenerating cycle, i.e., at least 6 – 7 weeks (Melissopoulos & Levacher 1998). Thus the purpose of the present work was to determine whether the cellular structures of hairless rat skin are affected during a 12-week chronic local exposure to GSM-900 and -1800  mobile phone radiation at around the two highest levels previously used of ca. 2 and 4 W/kg.
Material and methods Animals
Five-week-old hairless female rats  were used so that animals in the acute and chronic studies had the same age at the end of the study. The animals were housed under controlled temperature (228C) and lighting conditions (monitored light-dark cycles 08:00 – 20:00 h), and
supplied with water and food ad libitum (UAR 04, SAFE, Les Tremblats, 89290- Augy, France). The animals were kept for one week in the laboratory before starting the treatment. French regulations (Decree 87-848) regarding animal care, animal handling,and experiments on live animals were followed.  Eight rats, randomly distributed in each experimental group, were gradually accustomed to the rockettype
exposure set-up over one week (except control cage animals). This rocket type system consisted of a plastic tube-like structure which could be equipped with a loop antenna place on the right back of the animal. This loop antenna could be moved as the rat was growing. Thereafter, rocket-habituated animals were exposed or sham-exposed for 2 h per day, 5 days a week, for 12 weeks to GSM-900 or -1800
signals (ca. 2.5 or 5 W/kg SAR at skin level) using a loop-antenna (cf. the dosimetry section in the companion paper). The animals were sacrificed, using a lethal intra-peritoneal injection of urethane (3 mg/ml), 72 h after the last exposure, in order to observe stable chronic processes only. A skin biopsy was done not only at the selected location of the exposed backside, but also on the symmetrical part of the back in order to obtain an internal control.