Actinic Keratosis
An actinic keratosis (AK), also known as a solar keratosis, is a crusty, scaly growth caused by damage from exposure to ultraviolet (UV) radiation. You’ll often see the plural, "keratoses," because there is seldom just one. AK is considered a precancer because if left alone, it could develop into a skin cancer, most often the second most common form of the disease, squamous cell carcinoma (SCC).  More than 419,000 cases of skin cancer in the U.S. each year are linked to indoor tanning, including about 168,000 squamous cell carcinomas.

The most common type of precancerous skin lesion, AKs appear on skin that has been frequently exposed to the sun or to artificial sources of UV light, such as tanning machines. In rare instances, extensive exposure to X-rays can cause them. Above all, they appear on sun-exposed areas such as the face, bald scalp, ears, shoulders, neck and the back of the hands and forearms. They can also appear on the shins and other parts of the legs. They are often elevated, rough in texture and resemble warts.  Most become red, but some are light or dark tan, white, pink and/or flesh-toned. They can also be a combination of these colors.

In the beginning, AKs are frequently so small that they are recognized by touch rather than sight. They feel as if you were running a finger over sandpaper. Patients may have many times more invisible (subclinical) lesions than those appearing on the surface.

Most often, actinic keratoses develop slowly and reach a size from an eighth to a quarter of an inch. Early on, they may disappear only to reappear later. Occasionally they itch or produce a pricking or tender sensation. They can also become inflamed and surrounded by redness. In rare instances, AKs can even bleed.