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We agree that UV-B—induced tolerance is likely to depend on the spectral power distribution of the radiation source used to induce this tolerance. The spectral power distribution of the UV sources used in all phases of our study are typical of those used for phototherapy in the United States today. Therefore, our results are likely to reflect the degrees of tolerance achieved by most patients currently receiving UV-B phototherapy today. The sources noted by Drs Diffey and Farr are not used commonly in the United States today and might induce different degrees of tolerance. Since our UV-C source emits less than 5% UV-C, we doubt UV-C was an important contributor to the tolerance we observed.Diffey and Farr emphasize the contribution of stratum corneum thickening to tolerance and imply changes in the stratum corneum are likely to be the predominant factor in UV-induced tolerance. We believe the phenomenon of tolerance
Taylor CR, Stern RS. Magnitude of UV-B—Induced Tolerance-Reply. Arch Dermatol. 1992;128(3):411. doi:10.1001/archderm.1992.01680130133025