1. A focal, scaly excrescence on the scalp, face, neck, or other exposed surface of skin resulting, at least partially, from long exposure to the ultraviolet rays of the sun: "These actinic keratoses or solar keratoses are growths that are usually pink or red and appear as flaky, rough scaly patches or areas of skin and they may also be light gray or brown and feel hard, rough, or gritty.
2. Actinic keratoses (solar keratoses) are precancerous growths caused by long-term sun exposure.
3. Etymology: actinic is from Greek aktis, "ray" and refers to the ultraviolet rays, as in sunlight, that can cause reaction in the skin; so, a "sunbrn" is an actinic injury while keras is a Greek element for "horn".

Such conditions can be prevented by decreasing oneself to sun exposure and by wearing sunscreen.

Actinic keratoses usually can be removed by freezing with liquid nitrogen (cryotherapy); however, if a person has too many growths, a liquid or cream containing fluorouracil may be applied.

Often, during such treatment, the skin temporarily looks worse because fluorouracil causes redness, scaling, and burning of the keratoses and of the surrounding sun-damaged skin.

A relatively new drug, imiquimod, is useful in treating actinic keratoses because it helps the immune system to recognize and to destroy cancerous skin growths.

Another treatment includes cutting the keratoses away, by burning them with photodynamic therapy; that is, injecting into the bloodstream a chemical that collects in actinic keratoses and makes them more sensitive to destruction by a specialized form of light.