The Facts

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, that have been chronically exposed to the sun.

AK is a precancerous condition that affects only the top layer of skin (the epidermis). Ultraviolet (UV) from the sun damages the skin and if left untreated, actinic keratosis 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. Australia has the highest rate of AK in the world.

Causes

Ultraviolet (UV) light from the sun is the major cause 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.

Long-term exposure to the sun increases a person's risk of AK. That's why AK is more common in older people who have accumulated sun damage to their skin. AK can occur in younger people, but it is more common for those over 60 years old. People who work outdoors are also at higher risk.

Another risk factor for AK is skin type. AK most often occurs in people with fair skin and is rare in people with darker skin. People who develop AK tend to have red or blonde hair, and skin that burns easily and does not tan.

Symptoms and Complications

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 1000 AK lesions will become cancerous.

Making the Diagnosis

AK can look similar to other skin conditions such as psoriasis or skin cancer. Your doctor can usually diagnose AK with a physical examination, but sometimes a biopsy may be needed to make sure the lesion is not cancerous. A biopsy removes a small piece of tissue for testing. Biopsies may also be used to check lesions that have come back after treatment or that did not respond to treatment.

Treatment and Prevention

There are several options available for treating AK. Each one has its own advantages and disadvantages. Which one is best will depend on factors such as the size and location of the lesions, the number of lesions, and the person's overall health.

Cryotherapy uses a very cold substance, like liquid nitrogen, to freeze and kill the skin cells that make up the AK lesion. The liquid nitrogen is applied as a spray or with a swab. This treatment method is best for a small number of lesions.

Excision is surgical removal of the lesion using a sharp blade. Electrodessication and curettage dries out the AK cells with an electric current and then scrapes them out using a curette (a sharp instrument). These procedures require a local anesthetic. Like cryotherapy, these are not practical for large numbers of lesions.

Topical medications (medications that are applied to the skin) can be used to treat actinic keratoses and superficial basal cell carcinoma (sBCC). The topical medications currently available in Canada include 5-fluorouracil (also known as fluorouracil) and imiquimod. 5-fluorouracil (5-FU)* belongs to the group of medications known as topical antineoplastics. It works by interfering with cancer cell growth. It is applied to the skin in a thin layer and is then covered. The treatment is repeated daily over several weeks. This method is good for treating large areas of skin, but it takes a long time (2 to 4 weeks) to be effective. Women who are pregnant should not use 5-FU. Imiquimod is another topical medication for the treatment of actinic keratosis. It belongs to a new class of topical medications called immune response modifiers. This type of medication works by stimulating the immune system to produce substances that fight against the cancer. The treatment is applied to the skin twice a week for 12 weeks. This method is good for treating larger areas of skin.

Photodynamic therapy (PDT) uses light and a light-sensitizing medication to kill AK skin cells. The medication is applied to the skin and is absorbed by the abnormal AK cells more than the normal surrounding cells. The skin is then exposed to a specific colour of light that activates the medication and kills the cells. PDT is good for treating large areas of skin with many AK lesions.

Other possible treatments include:

• chemical peels
• dermabrasion
• laser treatment
• other topical medications (e.g., salicylic acid)

The best way to prevent AK is to avoid overexposure to the sun. Use a sunscreen with an SPF of at least 15, applied one-half hour before sun exposure and re-apply every two hours. Wear a hat and protective clothing to help protect your skin from the sun's UV rays. Remember to protect children as well. Try to stay out of the sun during peak hours (11 a.m. to 4 p.m.). It's important to make sure your sunscreen protects against both UVA and UVB rays.

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*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For more information on brand names, speak with your doctor or pharmacist.