An actinic keratosis (AK), also known as a solar keratosis, is a small, rough spot occurring on skin that has been chronically exposed to the sun. Actinic keratoses generally measure in size between 2-6 millimeters in diameter (between the size of a pencil point and that of an eraser). They are usually reddish in color, with a rough texture and often have a white or yellowish scale on top. Actinic keratosis often occurs against a background of sun damage, including sallowness, wrinkles, and superficial blood vessels.
In addition to feeling rough, actinic keratoses may feel sore or painful when fingers or clothing rub against them.
Specialized forms of actinic keratoses include cutaneous horns, in which the skin protrudes in a thick, hornlike manner, and actinic cheilitis, which refers to scaling and roughness of the lower lip and blurring of the border of the lip and adjacent skin.

Who is at risk for an actinic keratosis?

Those who develop actinic keratoses tend to be fair-skinned people who have spent a lot of time outdoors at work or at play over the course of many years or who have exposed their skin to indoor tanning. Their skin often becomes wrinkled, mottled, and discolored from sun exposure. Others at risk for developing actinic keratoses include those who have their immune systems suppressed, such as organ transplant patients, as well as patients with psoriasis treated with PUVA therapy (topical long-wave ultraviolet light plus oral chemicals called psoralens.)

Where on the body do actinic keratoses typically occur?

Common locations for actinic keratoses are the face, especially the cheeks and bridge of the nose, scalp, back of the neck, upper chest, as well as the tops of the hands and forearms. Men are more likely to develop AKs on top of the ears, whereas women's hairstyles often protect this area. AKs, especially on the scalp and the backs of the hands, may be hypertrophic (thickened skin).

What is the significance of an actinic keratosis?

Actinic keratoses are precancerous (premalignant), which means they can develop into skin cancer. However, relatively few of them actually become cancers, a process that typically takes years. When a malignant change does occur, the cancer is called a squamous cell carcinoma. Although squamous cell skin cancers have the potential for metastasis (spreading to other areas), such cancers that arise in preexisting actinic keratoses have a low potential for such spread, and only do so once they have gone deeper and the skin and become invasive. Treating actinic keratoses at an early stage helps prevent this possibility.
When patients are diagnosed with this condition, they often say, "But I never go out in the sun!" The explanation is that it takes many years or even decades for these keratoses to develop. Typically, the predisposing sun exposure may have occurred many years ago. Short periods of sun exposure do not generally either produce AKs or transform them into skin cancers.