[en] Under specific light illumination, particularly ultraviolet (UV) and near-UV light stimulation, the skin produces both specular light reflectance and, possibly, specific fluorescent emission. These properties offer diagnostic clues and disclose some peculiar functions of the skin. A series of superficial infections (erythrasma, some tinea capitis types, tinea/pityriasis versicolor, dermatophytoses, etc.) and pilosebaceous follicles enriched in Propionibacterium spp show fluorescence. This latter characteristic is downgraded or lost while on some anti-acne treatments. A quenching effect of fluorescence is observed following the application of sunscreens. The (pre)neoplastic areas prepared for methylaminolevulinate photodynamic therapy (MAL-PDT) show reddish fluorescence following drug metabolisation producing porphyrins by the abnormal activated cells. Of note, when using a recording sensitive CCD camera instead of casual visual observation, skin fluorescence may be superimposed on the specular reflectance of the incident light. With the current technology, these situations are not distinguished with confidence. Any harsh and scaly lesion appears brighter following yellowish specular light reflectance. Stratum corneum samplings collected on clear self-adhesive discs or cyanoacrylate skin surface strippings are conveniently examined ex vivo, taking advantage of the same optical properties.