Sunlight-induced Painful Skin (Sun Pain): A New Differential Diagnosis in Photodermatology

Photodermatoses are characterized by the development of skin eruptions following exposure to ultraviolet radiation or visible light. We report here the clinical findings and results of laboratory investigations and phototesting of 6 patients who experience debilitating and excruciating pain after sun exposure ("sun pain") in the absence of any skin eruption. Phototesting with sub-erythemal doses of ultraviolet A radiation triggered localized pain in 4 patients. At follow-up, 3 female patients were found to have developed fibromyalgia, 2 male patients experienced a major depressive disorder, and another male patient had a conversion disorder. One patient also developed allodynia to tactile stimuli and one developed allodynia to thermal and tactile stimuli. Psychiatric conditions should be taken into consideration in patients presenting with excruciating and debilitating pain on exposure to ultraviolet radiation, but with absence of skin eruption. Further research is needed to evaluate whether it represents a type of allodynia triggered by exposure to ultraviolet radiation.