Chemical phototoxicity in humans.

Phototoxic reactions may be induced by endogenous or exogenous chemicals. Endogenous photosensitizers made by the body include porphyrin molecules which are responsible for the photocutaneous syndromes noted in the porphyrias. Exogenous photosensitizers may arrive on the skin through topical applications or may be distributed through the vasculature. Topical photosensitizers are found in cosmetics, medications, plants, and industrial and air pollutant emissions. Systemic photosensitizers consist primarily of therapeutic agents. Acute and chronic phototoxic reactions may occur. The acute response is generally characterized by erythema and edema followed by hyperpigmentation and desquamation. The end point of chronic damage may be cutaneous cancer formation. The mechanisms of these changes may well relate to nucleic acid injury, protein and membrane damage, and alterations in other nuclear and cytoplasmic molecular structures. However, translation of experimental information into human responses remains to be clarified. A great deal of investigation is still needed in developing assays for detecting phototoxic chemicals and for defining mechanisms involved in phototoxic events in human skin.