Onset of polymorphous light eruption usually occurs in the first 30 yrs of life. This abnormality causes the body to form and excrete excessive amounts of heme metabolites. The actual photosensitivity begins in childhood on sun-exposed areas. Individuals who suffer from porphyria must be protected from solar radiation by a physical blocking agent or by clothing. Some porphyria sufferers respond to oral beta carotene.
Solar urticaria is a rare reaction to sun or UV exposure.
This is a true photoallergy. Wheals or vesicles appear. The actual mechanism that causes this reaction is unknown, however, antihistamines are effective in treating the reactions of some patients. This disease has been previously described as chronic photosensitivity dermatosis. It appears initially as red spots and patches in sun-exposed areas of the scalp, rim of the ears, back of the neck, forearms, and back of the hands.