Some patients with minimally to moderately thick actinic keratoses of the face and scalp are candidates for a treatment called photodynamic therapy (PDT). A chemical called Levulan is applied to the skin. After the Levulan sits on the skin for 45 minutes, the patient is given protective goggles and sits under a blue light for approximately 10-15 minutes. This light activate the Levulan, which helps clear the keratoses. The most common side effects include peeling, redness, or a burning sensation. Patients should avoid exposure of treated areas to sunlight or bright indoor lights for 48 hours after blue light treatment and wear sunscreen, even indoors. Exposure may result in a more extreme reaction.