Actinic keratoses are precancerous growths on the skin caused by long term exposure to ultraviolet radiation, usually in the form of sunlight or tanning beds. They frequently appear on sun exposure areas such as the scalp, face, back of the hands, and forearms, and are characterized by rough, dry lesions or patches that are easier to feel than to see. Because these precancers can develop into squamous cell carcinomas, treatment is recommended. Various treatment options are available including cryotherapy (using liquid nitrogen to freeze the precancer), topical medications, and photodynamic therapy (PDT).