The diagnosis of<unk>  is typically made by assessing the history and clinical observations. Any investigations are usually to exclude other conditions, particularly lupus and porphyria. Blood tests are usually normal. However, positive antinuclear antibody and extractable nuclear antigen (anti-Ro/La) in low titre may be found, even in the absence of other criteria to suggest a diagnosis of lupus erythematosus. If clinical findings suggest a possibility of porphyria, urinary and red cell porphyrin screening may be performed and are negative in<unk> . Photoprovocation tests are usually not required but may be undertaken by specialised centres in winter. When a decision to undertake this is made, a small area of the frequently affected skin is exposed to varying doses of UVA and minimal erythema dose (MED) (amount of UV radiation that will produce minimal redness of skin within a few hours following exposure) of broadband UVB for three consecutive days. An examination of the skin to detect the rash is made, however, up to 40% have false negative responses. Biopsy findings Depending on the clinical signs, histology of a skin biopsy may vary. There may be oedema in the epidermis with a dense superficial and deep lymphocytic infiltrate without vasculitis. Recently appearing lesions may show neutrophils. Spongiosis and vesicle formation may also be present. Direct immunofluorescence testing is negative. Differential diagnosis The photosensitivity connected with lupus erythematosus is the main condition that may appear like<unk> . However, the rash of lupus is inclined to be more persistent.<unk>  does not increase the risk of lupus. Other similar appearing conditions are solar urticaria, which has a shorter duration, the eczema-like condition, photosensitive dermatitis, and photosensitivity drug reaction. Prickly heat, which is caused by warm weather or heat is not the same as<unk> . Photosensitivity is also found in some of the porphyrias. Nearly all cases of porphyria cutanea tarda exhibit blister formation on the skin within 2–4 days of<unk>  exposure. Variegate porphyria and hereditary coproporphyria can also exhibit symptoms of<unk> -induced blisters. Classification Sunlight has been documented to trigger numerous skin conditions and the confusing terminology and categorisation previously has made the correct diagnosis and subsequent treatment difficult. Variants of<unk>  have been described: * Juvenile spring<unk>  is a cutaneous condition that affects the helices of the ears, particularly in boys, because their ears are relatively more exposed to sunlight. * Benign summer<unk><unk>  is a cutaneous condition, and a name used in continental Europe, particularly France, to describe a clinically short-lived, itchy, papular<unk>  particularly affecting young women after several hours of sunbathing at the beginning of summer or on sunny vacations. * Actinic Prurigo is a hereditary form of<unk>  occurring typically in native Americans.
Polymorphous light eruption
Lichenoid eruption
Acneiform eruption
Papuloerythroderma of Ofuji
Streptococcal intertrigo
Granulomatous facial dermatitis
Drug eruption
Poikiloderma of Civatte