Photosensitive psoriasis. An epidemiologic study.

In this study of photosensitivity among psoriasis patients, a questionnaire was mailed to 2000 psoriasis patients living within the service area of Karolinska Hospital, Stockholm. Of the 88% patients who replied, 4.4% stated that their psoriasis always worsened after sun exposure, and 7.3% stated that this was sometimes so. After telephone interviews with an 80% sample of these allegedly photosensitive patients, half of them were considered nonphotosensitive. Thus an estimated prevalence of 5.5% photosensitivity was obtained. Forty-three percent of the light-sensitive patients had a history of polymorphous light eruption with secondary exacerbation of psoriasis lesions. Comparison between the photosensitive and the nonphotosensitive patients concerning background factors and symptoms showed a statistically significant increase (p less than or equal to 0.001) in the photosensitive group concerning skin type I, psoriasis affecting hands, heredity for photosensitivity, and advanced age.