2. Possessing photochemical properties.
3. Pertaining to or designating radiant energy: "An actinic ray exists in the visible and ultraviolet spectrum which produces marked chemical changes."
"Actinic is a term for ultraviolet (UV) rays from sunlight and UV lamps."
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".
Solar keratoses, or senile keratosis, is more common with fair skinned and elderly people and it may be a discrete, slightly raised, red-on-pink lesion located on a sun-exposed surface.
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.