The exact cause of polymorphous light eruption is not totally clear. People affected by PMLE are sensitive to light, in particular, they are affected by the ultraviolet light spectrum. This sensitivity causes an immune system response that results in a rash. Genetics are suspected to play a role in the cause of PMLE. Polymorphic light eruption condition is the result of a delayed hypersensitivity reaction to a compound present in the skin that is altered by exposure to ultraviolet radiation. Patients with PMLE have a reduction in the normal UV–induced immune suppression in the skin, which causes the rash.
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