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March 1975

Ultraviolet Light Therapy for Psoriasis

Arch Dermatol. 1975;111(3):397. doi:10.1001/archderm.1975.01630150117023

To the Editor.—  In the April 1974 issue of the Archives, Drs. Stern and Kihiczak reported the results of their attempts to determine the action spectrum of ultraviolet light-induced clearing of psoriasis (109:502, 1974). Using a xenon arc solar simulator and a cold quartz lamp, the authors compared the clearing of psoriatic plaques that occurred after single or multiple exposures of UVC (254 nm), UVB (290-320 nm), UVA (320-400 nm), and a combination of UVA plus UVB in a ratio that was intended to simulate solar radiation. Using clinical and histologic criteria, a beneficial effect was observed only with the combination of UV-A + UV-B.To compare irradiation of different wavelengths, energy doses capable to inducing comparable erythema reactions must be used. The normal MED to UVB (MEDB) is 15 to 45 millijoules (mJ)/sq cm,1 while the MED to UVA (MEDA) is 1,000 times that of UV-B or 15 to

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