Photodynamic therapy (PDT) uses a photosensitizing drug (a substance that becomes activated by light exposure) and a light source to activate the applied drug. PDT essentially has three steps. First, a light-sensitizing substance, aminolevulinic acid (ALA) is applied to the skin. Second, there is an incubation period of several hours. Finally, the target skin is exposed to a specific wavelength of light (KTP), which activates the photosensitizing substance. PDT is an effective means of treating actinic keratosis or other skin imperfections, and significantly improves overall tone, texture and color. The skin will be red and peeling will occur for five to seven days post-procedure.