Les photoallergies graves

Photosensitivity reactions group together reactions to sunlight, in which the pathophysiology involves the subject's immune system. Concerning exogenous photosensitivity reactions, the photosensitizing molecules responsible for their development have been definitively identified and the reactions are known to be a form of classical delayed hypersensitivity. Nevertheless, while the photosensitizing molecules in idiopathic light eruptions (e.g., polymorphic light eruptions and chronic actinic dermatitis) have not been identified, here, the mechanism is now most often considered to be a delayed hypersensitivity; they can also be IgE-dependent (e.g., solar urticaria). The diagnosis of photosensitivity reactions rests on the patient's history, the appearance of the lesions, their histology and the results of a photo-testing examination. During an exogenous photosensitivity reaction, its severity will depend on the intensity of the reaction, on its evolution to chronic actinic dermatitis or even more on the severity of the specific condition (e.g., polymorphous erythema and hypersensitivity syndrome). Solar urticaria is a serious condition because of its disabling character, the difficulty of treating it and, occasionally, by the existence of general signs or its association with systemic diseases. Hydroa vacciniform (vacciniform cold sores) and pruriginous lesions can lead to the development of particularly ugly scars. More disturbing, vacciniform cold sores can be associated with latent EBV infection and may be complicated by lymphoproliferative disorders involving natural killer cells or by haemolytic syndromes. Chronic actinic dermatitis is surely the most severe photosensitivity reaction because of the severity of the photosensitivity and the risk of its evolution to a lymphoproliferative disorder.