II. Causes:

AKs are defined as a cutaneous dysplasia skin growth of the epidermis (the outermost layer of skin).  In everyday terms, AKs are an alteration in size, shape and organization of skin cells.  The cells most affected in AKs are the keratinocytes, the tough-walled cells that make up more than 90 percent of the epidermis and give the skin its texture.  Cellular alterations in AKs may extend into the dermis, the layer of skin under the epidermis. The most significant cause of actinic keratoses is long-term exposure to sunlight, and specifically to the ultraviolet wavelengths of solar radiation.  The most significant predisposing factor to AKs is fair skin.

The alteration in skin growth and differentiation of keratinocytes is manifested in the clinical features of AKs - rough, scaly skin, "bumps" on the skin, mottled skin, and cutaneous horn.  Alterations in cell growth and differentiation also set the stage for transformation of AKs into invasive squamous cell carcinoma.

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