title: Skin pigmentation kinetics after exposure to ultraviolet A.
abstract: Multiple exposures to ultraviolet radiation (UVR) are the norm in nature and phototherapy. However, studies of the kinetics of pigmentation following UVA exposure have included only fair-skinned persons. The aim of this study was to investigate steady-state pigmentation and fading in 12 Scandinavians and 12 Indians/Pakistanis after 6 and 12 exposures on the back using broadband UVA and UVA1 with equal sub-minimal melanogenic doses (individually predetermined). Pigmentation was measured by skin reflectance at 555 and 660 nm. The UV dose to minimal pigmentation was higher in dark-skinned persons after a single broadband UVA exposure, but independent of pigmentation/skin type after single and multiple UVA1 exposures. To elicit minimal melanogenic doses after 6 and 12 exposures, every dose is lowered by a factor of 2 and 3, respectively, but the cumulative dose increases three- and four-fold, respectively. The absolute increase in pigmentation was independent of pre-exposure pigmentation; therefore the percentage increase in pigmentation was higher in fair-skinned subjects. The absolute increase in pigmentation was higher and it took 2-3 days longer to reach steady-state after 12 UV exposures compared with 6 UV exposures. Days to steady-state pigmentation and fading were independent of pre-exposure pigmentation, and fading took 5-6 months. Comparing data from a narrowband UVB source and a Solar Simulator, it was shown that pigmentation built up faster and increased more after 12 UVA exposures (16 days) than with the Solar Simulator (21 days).
authors.affiliation: Department of Dermatology, Bispebjerg Hospital, University of Copenhagen, DK-2400 Copenhagen NV, Denmark.
authors.forename: Mette H
authors.initials: MH
authors.lastname: Ravnbak
authors.forename: Peter A
authors.initials: PA
authors.lastname: Philipsen
authors.forename: Stine R
authors.initials: SR
authors.lastname: Wiegell
authors.forename: Hans C
authors.initials: HC
authors.lastname: Wulf
mesh_terms: D000328:Adult; D004307:Dose-Response Relationship, Radiation; D004781:Environmental Exposure; D004890:Erythema / Q000209:etiology; D005006:Ethnicity; D005260:Female; D006801:Humans; D008297:Male; D012537:Scandinavian and Nordic Countries; D012880:Skin Pigmentation / Q000502:physiology / Q000528:radiation effects*; D014466:Ultraviolet Rays; D055815:Young Adult