title: Impact of epidermal thickness on purpura from the pulsed dye laser.
abstract: OBJECTIVE
  To clarify whether epidermal thickness is of importance to the purpuric reaction from treatment with the pulsed dye laser (PDL).
  
  
  METHODS
  Fifteen fairly pigmented volunteers were laser treated in two test regions of varying epidermal thicknesses: normal buttock skin and ultraviolet B (UVB)-exposed buttock skin. Laser treatments were performed with the flashlamp-pumped PDL (585 nm). Fluences ranged from 3-6.5 J/cm2, spot size was 7 mm, and each volunteer received at least six fluences in each treatment region. Assessment of the response was based on clinical evaluation (threshold dose to purpura 10 minutes and 1 day after treatment) and skin reflectance-evaluated redness (1 and 6 days, 2 and 6 weeks after treatment).
  
  
  RESULTS
  The total epidermal thickness differed between the unexposed buttock skin (median, 72.7 microm) and the UVB-exposed buttock skin (87.2 microm) (P < 0.01). There was no correlation between the epidermal thickness and the threshold dose to induce purpura 10 minutes and 1 day after laser exposure. Skin reflectance revealed no correlation between the epidermal thickness and the skin reflectance evaluated redness on 1, 6 days, and 2 weeks postoperatively. A dose-response relation was seen within the two test regions; 6 weeks after laser exposure, there was no remaining laser-induced skin redness.
  
  
  CONCLUSIONS
  The epidermal thickness is unimportant to the purpuric reaction after PDL treatment.
authors.affiliation: Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Haedersdal
authors.forename: N
authors.initials: N
authors.lastname: Bech-Thomsen
authors.forename: P
authors.initials: P
authors.lastname: Therkildsen
authors.forename: T
authors.initials: T
authors.lastname: Poulsen
authors.forename: H C
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D000328:Adult; D004817:Epidermis / Q000473:pathology*; D006801:Humans; D053685:Laser Therapy / Q000009:adverse effects* / Q000379:methods; D017078:Laser-Doppler Flowmetry; D011693:Purpura / Q000209:etiology* / Q000473:pathology; D012016:Reference Values; D018709:Statistics, Nonparametric; D014466:Ultraviolet Rays / Q000009:adverse effects