Do you have Actinic Keratosis (AK)? AKs are often called sun spots. They range in colour from skin toned to reddish brown. AKs are rough textured, dry, scaly non-healing patches on the skin that are caused by excessive exposure to ultraviolet light, such as sunlight. If left untreated, AKs can potentially develop into skin cancer. Photodynamic Therapy, more commonly known as PDT, is a non-invasive and gentle medical treatment that is used to combat the effects of sun damage with impressive results.