RT Book, Section A1 Lim, Henry W. A2 Kang, Sewon A2 Amagai, Masayuki A2 Bruckner, Anna L. A2 Enk, Alexander H. A2 Margolis, David J. A2 McMichael, Amy J. A2 Orringer, Jeffrey S. SR Print(0) ID 1161327403 T1 Phototoxicity and Photoallergy T2 Fitzpatrick's Dermatology, 9e YR 2019 FD 2019 PB McGraw-Hill Education PP New York, NY SN 9780071837798 LK accessmedicine.mhmedical.com/content.aspx?aid=1161327403 RD 2024/03/29 AB AT-A-GLANCEPhotosensitivity to exogenous agents is broadly divided into phototoxicity and photoallergy; it is caused by topical or systemic agents that absorb ultraviolet A (UVA) radiation.Phototoxicity occurs in anyone exposed to sufficient doses of phototoxic agent and UV radiation; it usually manifests as an exaggerated sunburn reaction.Photoallergy is an immune reaction to a UVA-modified chemical, commonly topical sunscreen agents and antimicrobials in the United States and the United Kingdom, and topical nonsteroidal antiinflammatory agents in Europe. It presents as eczematous eruption on sun-exposed areas.Phototoxicity and photoallergy do occur in patients with skin of color, frequently resulting in postinflammatory hyperpigmentation.History taking is an important part of the evaluation; phototesting and photopatch testing are sometimes helpful.Differential diagnosis includes contact allergic or contact irritant dermatitis, airborne contact dermatitis, and other photodermatoses.Management consists of identification and avoidance of the precipitating agent, photoprotection, and symptomatic therapy.