Photodynamic therapy (PDT) is a medical treatment that uses a photosensitizing drug (a drug that becomes activated by light exposure) and a light source to activate the applied drug. The result is an activated oxygen molecule that can destroy nearby cells. Precancerous cella, certain types of cancer cells and acne can be treated this way. The procedure is easily performed in a physician's office or outpatient setting. 

PDT essentially has three steps. First, a light-sensitizing liquid, cream, or intravenous drug (photosensitizer) is applied or administered. Second, there is an incubation period of minutes to days. Finally, the target tissue is then exposed to a specific wavelength of light that then activates the photosensitizing medication.