Photodynamic therapy (PDT) is a preventative treatment that targets sun damage and precancerous cells in the skin. A medicine is applied to the area to be treated and allowed to sit in place for a designated period of time (incubation). After the incubation period, a light is used that specifically activates the medication that was applied. This causes a burning sensation during the treatment which varies in intensity from patient-to-patient. After the treatment, the skin can become red and swollen, similar in appearance to a sunburn. Over the next seven to 10 days the skin peels and the redness resolves. While patients do not always achieve 100 percent clearance, PDT does typically result in a substantial reduction of precancerous changes in the skin. Skin cancer prevention is the goal.