1. A reference to radiation, such as sunlight or x-rays: A sunburn is an actinic burn while actinic keratosis is a skin lesion that is caused by chronic sun exposure.
2. Regarding photochemical properties: Some actinic attributes are found in containers that protect them from photo-degradation.
3. Pertaining to or designating radiant energy: An actinic ray exists in the visible and ultraviolet spectrum which produces marked chemical changes.

An injury to the skin caused by exposure to a source of ultraviolet radiation: An actinic burn is sometimes a painful redness of the skin caused by having a person's bare skin out in plain view of the sun for too long.

A basal cell or squamous cell cacinoma of the face and other exposed surfaces of the body: Actinic carcinoma is seen in people who spend prolonged periods of time in direct sunlight.

An inflammation of the conjunctiva (transparent membrane covering the eyeball): Actinic conjunctivitis can be caused by exposure to the ultraviolet radiation of sunlight or other sources, such as exposure to acetylene torches, therapeutic lamps (sun lamps), and klieg lights (powerful carbon-arc lamps producing intense light and used especially in making movies).

"Actinic" is the adjective referring to ultraviolet (UV) rays from sunlight and UV lamps.

A skin inflammation or rash resulting from exposure to sunlight, X-rays, or atomic particle radiation: Chronic or recurrent actinic dermatitis can lead to skin cancer.

Inflammation of the conjunctiva and cornea: Actinic keratoconjunctivitis includes pain, photophobia, lacrimation, and smarting of the eyelids caused by repeated flashes of bright light or ultraviolet radiation.

1. A pe-cancerous focal, scaly excrescence on the skin; solar keratoses; senile keratosis; senile wart: Actinic keratosis can affect 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. 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 keratosis 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 keratosis because it helps the immune system to recognize and to destroy cancerous skin growths.

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

An itching which returns each summer, becoming very severe as long as the hot weather continues.