Photodynamic therapy (PDT) is an effective treatment for pre-cancerous lesions on the skin also known as actinic keratoses. Left untreated, they can eventually develop into skin cancers. The first step is the application of a photosensitizing medication called levulan which is selectively absorbed by pre-cancerous and cancerous skin cells, making them more sensitive to light. After waiting for the levulan to be absorbed (30 minutes to 2 hours), the treatment area is exposed to a light for a short time, which activates the levulan, and destroys the targeted lesions. It is very important to avoid exposure to bright light and/or direct sunlight during the 48 hours after the treatment. The results of the treatment are often maintained for many years if careful sun protection is followed thereafter.