Actinic keratosis (also called solar keratosis and senile keratosis is a pre-cancerous patch of thick, scaly, or crusty skin. These growths are more common in fair-skinned people and those who are frequently in the sun. They usually form when skin gets damaged by ultraviolet (UV) radiation from the sun or indoor tanning beds. AKs are considered potentially pre-cancerous; left untreated; they may turn into a type of cancer called squamous cell carcinoma. Untreated lesions have up to a 20% risk of progression to squamous cell carcinoma, so treatment by a dermatologist is recommended. Development of these growths occurs when skin is constantly exposed to the sun over time. They usually appear as thick, scaly, or crusty areas that often feel dry or rough. In fact, AKs are often felt before they are seen, and the texture is often compared to sandpaper. They may be dark, light, tan, pink, red, a combination of all these, or have the same color as the surrounding skin. An actinic keratosis lesion commonly ranges between 2 and 6 millimeters in size but can grow to be a few centimeters in diameter. They often appear on sun-exposed areas of the skin, such as the face, ears, neck, scalp, chest, backs of hands, forearms, or lips. Because they are related to sun-damage on the skin, most people who have an AK have more than one.