RT Book, Section A1 Wolff, Klaus A1 Johnson, Richard Allen A1 Saavedra, Arturo P. A1 Roh, Ellen K. SR Print(0) ID 1140790072 T1 PHOTOSENSITIVITY, PHOTO-INDUCED DISORDERS, AND DISORDERS BY IONIZING RADIATION T2 Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology, 8e YR 2017 FD 2017 PB McGraw-Hill Education PP New York, NY SN 9781259642197 LK dermatology.mhmedical.com/content.aspx?aid=1140790072 RD 2024/03/29 AB The term photosensitivity describes an abnormal response to sunlight. Cutaneous photosensitivity reactions require absorption of photon energy by molecules in the skin. Energy is either dispersed harmlessly or elicits chemical reactions that lead to clinical disease. Absorbing molecules can be: (1) exogenous agents applied topically or systemically, (2) endogenous molecules either usually present in skin or produced by an abnormal metabolism, or (3) a combination of exogenous and endogenous molecules that acquire antigenic properties and thus elicit a photoradiation-driven immune reaction. Photosensitivity disorders occur only in body regions exposed to solar radiation (Fig. 10-1).