Polymorphic light eruption (PLE) is a photodermatosis (i.e. "sun allergy") with a high prevalence, particularly among young women in temperate climates. It is characterized through itchy skin lesions of variable morphology, occurring in spring or early summer on sun exposed body sites. As yet the exact etiology and pathogenesis of PLE are unknown although a resistance to ultraviolet (UV)-radiation-induced immunosuppression (i.e. a physiologic phenomenon in normal healthy subjects) and a subsequent delayed type hypersensitivity (DTH) response to a UV-modified skin antigen (i.e. neo-antigen) has been suggested as a key factor in the disease. This article reviews the cellular and molecular disturbances associated with and most likely playing a role in pathogenesis of the disease.