PHOTODYNAMIC THERAPY (PDT) is a treatment that combines a photosensitizing molecule and a light source (blue light) to selectively target and destroy atypical skin cells (actinic keratoses). It is especially useful for large areas of sun-damaged skin. Following treatment, we advise to stay indoors and avoid sunlight for 24 -48 hours. Direct sunlight in the first 1 - 2 days may lead to an exuberant red reaction. PDT is also an effective treatment for acne, photoaging and rejuvenation. For these latter indications, insurance coverage is not expected.