Narrow-band (TL-01) UVB lamps are being increasingly used for phototherapy in cases of psoriasis and other dermatoses due to the excellent results obtained. However, in Korea many patients receiving phototherapy have complained about the tanning effect of ultraviolet radiation.
The aim of this study was to determine the time-course of pigmentation induced by phototherapy during and after narrow-band UVB treatment.
Changes in skin color were recorded during phototherapy in 40 patients and after treatment in 20 patients. All patients were Korean and were evaluated during 10 weeks of phototherapy (three sessions per week), and then weekly post-phototherapy using two different reflectance spectrophotometers for 10 weeks. Results are presented as erythema (E)- and melanin (M)-indexes and as L*a*b* values as recommended by the Commission Internationale de l'Eclairge and individual typology angle (ITA).
L* values, which indicate luminance, decreased continuously over the 5 weeks of phototherapy and showed a plateau after 5 weeks of treatment, and then slowly recovered over 10 weeks of post-treatment observation. Patterns of a* and b* values were comparable with L* values both during and after therapy. Mean ITA values also showed a pattern similar to L* values. E and M indexes changed slowly both during and post-phototherapy. In addition, when data were analyzed by skin type, the different skin types showed temporal patterns similar to the overall skin values, but the L* values and ITA and M indexes of skin type III recovered faster than those of skin types IV or V.
This study shows that pigmentation induced by narrow-band UVB phototherapy increases continuously during the therapy and that recovery requires 10 weeks or more.