What is Photosensitivity Disease?

Diagnosis of photosensitivity disease may be very difficult and need careful history about the duration of exposure to sun as well as duration of the signs and symptoms, the length of time between exposure to sunlight and the development of signs & symptoms (subjective complaints), and visible changes in the skin. Some times age of onset can be very helpful in diagnosing a photosensitivity disease; e.g. acute photosensitivity of erythropoietic protoporphyria generally (almost always) begins during childhood, whereas the chronic photosensitivity of porphyria cutanea tarda (PCT) usually begins in the fourth and fifth decades of life.

A history of exposure to drugs (both topical and systemic) and chemicals can provide important clue in diagnosing a photosensitivity disease. Many groups of drugs can cause photosensitivity by phototoxicity or by photoallergy. There are many chemicals which can cause photosensitization like fragrances like musk ambrette (were previously used in numerous cosmetic products).

Examination of skin carefully is an essential part of diagnosing a photosensitivity disease. A photosensitivity disease generally spare an area of skin which is not generally exposed to sun (naturally protected from direct sunlight) like scalp, the upper eyelids, the some areas of ear and submental regions etc. but the exposed parts can show features of photosensitivity process. Sometimes the location of skin lesion gives a clue to diagnosis.

There are many diseases which can be aggravated by exposure to direct sunlight, like lupus erythematosus (systemic, discoid etc.). Even in diseases aggravated by exposure to sun may have some genetic reason (genetic abnormalities ranging from well-described defects in DNA repair that occur in the inherited abnormalities in heme synthesis that characterize the porphyrias) behind it.

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