Repeated, prolonged sun exposure causes skin damage, especially in people with fair colored skin. Sun damaged skin becomes dry and wrinkled, and may form rough, scaly spots, called actinic keratoses. Treatment of actinic keratoses requires removal of the abnormal skin cells. New skin then forms from the deeper skin cells, which have escaped sun damage. They are very common on sites repeatedly exposed to the sun, especially the backs of the hands, scalp, nose, cheeks, upper lip, temples and forehead. They appear as multiple flat or thickened, scaly or warty, skin colored or red lesions. A keratosis may thicken and grow over time and develop into a cutaneous horn. These lesions are considered precancerous and remain on the skin even though the crust or scale is picked off.

The main concern is that actinic keratoses may give rise to a type of skin cancer called squamous cell carcinoma. The risk of squamous cell carcinoma occurring in a patient with more than ten actinic keratoses is about 10 to 15%. Actinic keratoses are usually removed because they are unsightly, uncomfortable, and because of the risk that skin cancer may develop in them. If an actinic keratosis becomes thickened, painful or ulcerated, get it checked. It may have developed into a skin cancer. Depending on the location, number and thickness of the lesion, treatment options include liquid nitrogen, curettage, excision, 5-fluorouracil cream, Imiquimod cream, photodynamic therapy, and Ingenol mebutate gel. 

The best defense against actinic keratoses is a comprehensive sun protection program that includes wearing sun protective clothing, avoiding midday sun, staying in the shade as much as possible, and wearing a broad–spectrum sunscreen with a sun protection factor (SPF) of at least 30.