title: Do we alter ultraviolet sensitivity in vivo with stratum corneum rehydration? A pilot study and review of the literature.
abstract: BACKGROUND
  Numerous therapeutic schemes recommend topical administration of emollients immediately prior to ultraviolet (UV) B therapy. The rationale behind the clinical improvement is a presumed enhancement of UV transmission through the epidermis. Originating from this clinical observation, there has been some concern as to whether a well-hydrated skin in general might be more susceptible to actinic damage.
  
  
  OBJECTIVE
  To investigate whether rehydration of healthy skin causes an altered UVB sensitivity in vivo.
  
  
  METHODS
  We determined minimal erythema doses (MEDs) and erythema sum scores (ESSs) after differential rehydration of the skin in 10 healthy volunteers. In each subject six UVB phototests were performed after pretreatment with five different emulsifying ointments (unguentum emulsificans and dilutions with 30, 50, 70 and 90% aqua purificans) plus a negative control. In vivo evaluation of stratum corneum hydration was performed by measurement of electrical capacitance.
  
  
  RESULTS
  The results of this randomized, double-blind in vivo study indicated that rehydration of normal stratum corneum with the emulsifying ointments tested did not result in a significantly altered sensitivity to the erythematous effects of UVB irradiation (no significant differences in MED and ESS). Furthermore, there was no correlation between measured stratum corneum hydration and the erythema response of healthy skin.
  
  
  CONCLUSIONS
  Although many schemes recommend the administration of emollients prior to UV therapy, there have also been calls for caution, as an uncritical application may interfere with such treatment. We showed that the emulsifying ointments tested exhibited no photoprotective potential and thus are suitable for the pretreatment of psoriasis prior to phototherapy. It has long been discussed whether the effects of emollient pretreatment on response to UV occur only in psoriatic skin or also in healthy skin. Our results indicated that stratum corneum rehydration did not result in a significantly increased erythema response of healthy skin to UVB exposure. With regard to the use of rehydrating cosmetics in everyday life, the outcome of our pilot study is reassuring, as we could not confirm with our experimental design that well-hydrated healthy skin is more prone to actinic damage.
authors.affiliation: University of Hamburg, Department of Cosmetic Sciences, von Melle Park 8 (FB 13), D-20146 Hamburg, Germany.
authors.forename: S C
authors.initials: SC
authors.lastname: Behrens-Williams
authors.forename: D
authors.initials: D
authors.lastname: Kraus
authors.forename: T
authors.initials: T
authors.lastname: Reuther
authors.forename: M J
authors.initials: MJ
authors.lastname: Kerscher
mesh_terms: D000328:Adult; D001834:Body Water / Q000378:metabolism*; D004307:Dose-Response Relationship, Radiation; D004311:Double-Blind Method; D004643:Emollients / Q000494:pharmacology*; D004817:Epidermis / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects*; D004890:Erythema / Q000209:etiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011832:Radiation Injuries / Q000209:etiology; D014467:Ultraviolet Therapy / Q000009:adverse effects
chemical_list: D004643:Emollients