A sensor for detecting the presence of skin is disclosed, one configuration of which uses multiple light emitting diodes, each of a unique wavelength band, and a broad-band photodetector to measure the remission of light at multiple wavelengths from a material being analyzed. Characteristics of the spectral remission of the material are used to discriminate human skin from materials that are not human skin. Further, an aesthetic medical device utilizing such a sensor in which the device is inhibited from operation if skin has not been detected. The incorporation of a skin sensor improves the safety of devices that emit radiation that otherwise would pose a hazard if not directed onto skin.