History: Chronic actinic dermatitis encompasses 4 diagnoses: actinic reticuloid, photosensitive eczema, photosensitivity dermatitis, and more recently, persistent light reactivity.  The diagnosis of CAD is distinct from that of compositae dermatitis or other types of contact dermatitis and from photoallergic contact dermatitis. However, both contact and photoallergic contact dermatitis seem to predispose to, and are associated with, the development of sensitivity to UV light, as indeed do other forms of eczema such as endogenous eczema, such that the patient then reacts to UV light alone in the absence of allergen.  Immunohistochemical studies have confirmed that CAD is a T-cell driven, type IV immune response.