Polymorphic light eruption on the arm

The cause of polymorphous light eruption is unknown. It usually appears 1 to 2 days following exposure to sunlight and may last up to one week. It is more common during adolescence and young adulthood, and occurs more frequently in females. It appears as recurrent redness (erythematous) and/or blistered patches (plaques). It may be an inherited disease in certain Native American groups.