Actinic Keratosis
(Precancerous Skin Lesion · Solar Keratosis)
In this condition factsheet:
The Facts on Actinic Keratosis
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). This percentage increases significantly in people who have more than 5 AK lesions. When they are found early, AKs are highly treatable.
AK is more common in people with fair skin. About 60% of all Canadians over the age of 40 have at least one AK lesion. Australia has the highest rate of AK in the world.
Causes of Actinic Keratosis
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.
Risk factors include:
- age 40 and older – AK can happen at any age, but the risk increases with accumulated sun exposure
- immunosuppression – the body's ability to recognize and fight abnormal cells are lowered in people with weak immune systems (e.g., as a result of taking organ transplant medications or chemotherapy, or having AIDS), so cells with gene changes are allowed to grow and form lesions
- people with fair skin – also people who have red or blonde hair and those who tend to burn rather than tan develop AK more easily
- sun exposure – people who work outdoors or have more exposure to the sun are at higher risk
Symptoms and Complications of Actinic Keratosis
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 firmer than other AK lesions are more likely to become skin cancer. About 10% of all AK lesions will become cancerous if left untreated for too long.
