In Vivo Damage Induced bu UV in the Epidermis of the Scalp

the minimum erythematous dose (DEM) will be calculated using a solar irradiator on the scalp (study area) and on a forearm (control area). On D2 (D1+24h) a solar irradiation corresponding to 2 DEM will be performed on a region of the scalp (studied area), as well as on a forearm (control area). A 3mm biopsy will be performed 15mn after irradiation in these 2 regions to study DNA damage. At D4 (D2+48h) a 2nd biopsy of 3 mm will be performed to study the repair of induced DNA damage.