Keratosis, actinic: A small rough spot on the skin that can give rise to a skin cancer called squamous cell carcinoma. Actinic keratosis is due to excessive sun exposure and most frequently occurs in fair-skinned people after 40 years of age. Common locations for actinic keratosis are the face, scalp, nape of the neck, upper chest, forearms, and backs of the hands. Prevention involves minimizing sun exposure and using sunscreen. Treatments include cryosurgery (freezing), surgical removal, topical medications, laser therapy, and photodynamic therapy (injection into the bloodstream of a chemical that collects in the actinic keratoses to make them more sensitive to exposure to a specialized form of light). Also known as senile keratosis and solar keratosis.