title: Investigation of cutaneous photoadaptation to narrowband ultraviolet B.
abstract: BACKGROUND
  Photoadaptation describes the skin's ability to withstand an increased dose of ultraviolet (UV) radiation with repeated exposure, and this is the reason for exposure doses being increased during a course of phototherapy. However, directly measured data on photoadaptation are available only for broadband (BB) and not narrowband (NB)-UVB.
  
  
  OBJECTIVE
  To measure photoadaptation to narrowband UVB.
  
  
  METHODS
  We measured the degree of photoadaptation in patients with psoriasis during a standard course of NB-UVB phototherapy. The minimal erythemal dose (MED) was measured before and towards the end of a course of phototherapy. An adaptation factor (AF) was calculated for each patient using the ratio of final MED to initial MED. Sigmoid dose-response curves were also constructed.
  
  
  RESULTS
  MED results were available for 50 patients (mean age 44 years, 28 female). The mean AF was 2·7 (95% confidence interval 2·4-3·0). There was no significant correlation between AF and skin type or initial MED. Dose-response curves were right shifted and parallel after phototherapy, and there was no significant difference in the maximum slope (P = 0·73).
  
  
  CONCLUSIONS
  The photoadaptation caused by NB-UVB is considerably less than that reported for BB-UVB. The variation in photoadaptation between patients was not explained by skin type or baseline MED. Physical factors (such as tanning and epidermal thickening) are probably sufficient to account for photoadaptation, rather than downregulation of the inflammatory response. These data should help in the design of phototherapy protocols for NB-UVB to achieve optimal clearance of psoriasis.
authors.affiliation: Royal Victoria Infirmary, Newcastle upon Tyne, U.K.
authors.forename: S
authors.initials: S
authors.lastname: Darné
authors.forename: L C
authors.initials: LC
authors.lastname: Stewart
authors.forename: P M
authors.initials: PM
authors.lastname: Farr
authors.forename: P J
authors.initials: PJ
authors.lastname: Hampton
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects*; D000328:Adult; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D011565:Psoriasis / Q000532:radiotherapy; D011874:Radiometry; D012867:Skin / Q000528:radiation effects*; D014466:Ultraviolet Rays; D014467:Ultraviolet Therapy / Q000379:methods