(also called solar keratosis) is a precancerous skin lesion usually caused by too much sun exposure
. (It may also be caused by many other factors, such as radiation or arsenic exposure.) If left untreated, actinic keratoses can develop into a more invasive and potentially disfiguring skin cancer
called squamous cell carcinoma
. They appear predominantly on sun-exposed skin, such as the face, neck, back of the hands and forearms, upper chest, and upper back. Men may develop keratoses along the rim of the ear.