Actinic keratosis (AK) is a lesion that forms on sun-damaged skin. The lesions are small scaly patches on parts of the body, such as the face, ears, bald scalp, arms, and hands, which have been chronically exposed to the sun.
AK is a precancerous condition that affects only the top layer of skin (the epidermis). Ultraviolet (UV) rays from the sun damages the skin and if left untreated, 15% of AK can turn into a form of skin cancer called squamous cell carcinoma (SCC). When they are found early, AKs are highly treatable.
AK is more common in people with fair skin. It is found in 15% of people in North America and Europe. Australia has the highest rate of AK in the world.
UV light from the sun and commercial tanning lamps or beds are the major causes of AK. UV light causes changes in the genetic material of the skin's cells. Changes in certain genes can cause cells to grow abnormally and form lesions. There is some link between infection with human papillomavirus (HPV) and AK, but this is not yet proven.
Risk factors include:
AK lesions are small scaly patches that can be flat or slightly raised. They can range in colour from one's skin tone to a reddish-brown colour. They are about 3 mm to 10 mm across and may gradually enlarge. The skin around the lesions may show other signs of sun damage such as dark blotching, broken blood vessels, and a yellowish tinge.
Over time, AK lesions may become thicker and harder. Their colour may change from red to brown. Sometimes, a cone-shaped growth occurs above the skin surface at the site of the lesion. This is called a cutaneous horn.
The most common site for AK is the face, but it can occur anywhere on the body that has had long-term sun exposure, such as the arms, legs, and back of the hands. Sunbathers, for example, may develop AK on other parts of their bodies.
The most significant complication of AK is skin cancer. Once the AK lesion invades the lower layer of the skin (dermis), it is classified as squamous cell carcinoma (SCC), a form of cancer. If not treated, the cancer may spread to other areas of the body. Lesions that are more red, raised, and firm than other AK lesions are more likely to become skin cancer. About 1 in 1,000 AK lesions will become cancerous.