[How I explore...skin by photodiagnosis using skin fluorescence and its functional imaging].

Under specific light illumination, skin produces peculiar fluorescent aspects. Such property can be used to provide diagnostic arguments or to disclose some peculiar functions of the skin. Some superficial infections (erythrasma, tinea versicolor, dermatophytic tinea,..) reveal fluorescence that may be intense. The pilosebaceous follicles enriched in Propionibacterium spp show fluorescence. Such property is lost during some anti-acne treatments. A quenching effect is observed after application of sunscreens. The (pre)neoplastic areas prepared for dynamic phototherapy become fluorescent. Pyranine labeling of the stratum corneum exhibits fluorescence allowing the assessment of the renewal activity of the epidermis.