Chronic actinic dermatitis (CAD), which includes persistent light reaction, actinic reticuloid, photosensitive dermatitis, and photosensitive eczema, is a photodistributed eczematous dermatitis without a known photosensitizing agent that persists for more than 3 months.

Although the etiology is unclear, one proposed pathophysiologic mechanism is that CAD results from photoinduced modification of endogenous cutaneous antigen(s).

CAD is most commonly seen in men aged older than 50 years, with a long history of either occupational or recreational outdoor activities. The condition can be seen in women and also rarely in younger patients. Affected patients of all ages often have a history of atopic dermatitis and/or a history of allergic contact dermatitis and thus have a baseline tendency for delayed-type hypersensitivity reactions. CAD can occur in any skin type and anywhere in the world, although it is more commonly seen in patients with Fitzpatrick skin types V and VI and in temperate climates.

CAD may be a presenting sign of HIV infection, especially in younger CAD patients. If the diagnosis of CAD is considered, testing for HIV is recommended for patients with positive risk factors for HIV.