Photodynamic therapy (PDT) is a treatment for severe sun damage and precancerous skin growths. A topical medication known as a photosensitizer is applied to the treatment area and allowed to incubate on the skin surface. That skin site is then exposed to a light source that activates the medication and destroys atypical skin cells causing them to gradually scab and resolve. The skin will be exquisitely sensitive to the sun and all intense direct light for 48 hours following treatment. While treatment is essentially painless, it will result in varying degrees of redness and crusting depending on the extent of sun damage and precancerous growths. PDT is an excellent option for preventing the evolution of pre-cancers (actinic keratoses) to full blown skin cancers and therefore is particularly useful in patients with a history of non-melanoma skin cancer (basal cell carcinoma or squamous cell carcinoma).