Photodynamic Therapy ButtePhotodynamic therapy (PDT) is a minimally invasive procedure used to treat acne and precancerous skin lesions. PDT uses a topical photosensitizer called Levulan, which is applied to the skin and allowed to incubate for a specified amount of time. The skin is then exposed to a specific light energy in order to activate the medication and destroy the targeted cells. The medication remains active for up to 48 hours and, therefore, strict avoidance of sunlight and bright light is necessary for the 48 hours from the time that the Levulan was applied to the skin. Two or three treatments are often needed, scheduled four or more weeks apart, and can produce a profound improvement in acne. Maintenance treatments can be performed as needed, once the acne is under control.