title: Dislodgeable stratum corneum exfoliation: role in percutaneous penetration?
abstract: BACKGROUND
  Stratum corneum (SC) readily dislodgeable exfoliation could affect percutaneous absorption and thus influence treatment and toxicological effects. Urea, a classical enhancer, is absorbed less than 1% in vivo in man and might be a useful marker to quantify chemical-drug exfoliation. This study develops a simple model utilizing washing and tape-stripping to quantify surface loss of chemicals topically applied on human skin and estimate the extent of chemical-drug SC exfoliation.
  
  
  METHODS
  Urea, 10% as a model hydrophilic chemical marker, was applied to human skin on identical sites (5 cm(2)/area with 1.8 mg/cm(2) urea) in vitro and in vivo. At time points 0, 4, and 6 h, the area was washed, rubbed, and stripped five times with cellophane tape. Quantitative urea was performed by colorimetric assay.
  
  
  RESULTS
  The data of the in vitro protected non-exfoliating model, as the control, showed no statistical difference between 0-, 4-, and 6-h recovery (P > 0.05). In the air-exposed model in vivo exfoliation in man, the recovery decreased from 98.8 ± 3.7% to 93.9 ± 6.8% in 4 h and 86.4 ± 3.0% in 6 h (P = 0.02). In the cloth-covered model in vivo, the recovery decreased from 99.4 ± 5.8% to 84.9 ± 5.3% in 4 h (P = 0.04), which reached 73 ± 2.8% within 6 h (P = 0.007).
  
  
  CONCLUSIONS
  This study suggests that urea, measured with washing, rubbing, and tape-stripping, can be used as a possible chemical-drug SC readily dislodgeable exfoliation and friction rubbing metric. In addition, this might help to determine the rule of skin exfoliation in dermatopharmacologic and dermatoxicologic assessment.
authors.affiliation: Department of Dermato-Venereology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Zheng
authors.forename: Aline
authors.initials: A
authors.lastname: Vieille-Petit
authors.forename: Stephanie
authors.initials: S
authors.lastname: Chodoutaud
authors.forename: Howard I
authors.initials: HI
authors.lastname: Maibach
mesh_terms: D002102:Cadaver; D003873:Dermatitis, Exfoliative / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D003880:Dermatology / Q000379:methods; D005260:Female; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D066298:In Vitro Techniques; D008297:Male; D012869:Skin Absorption / Q000502:physiology*; D012879:Skin Physiological Phenomena / Q000187:drug effects; D013997:Time Factors; D014508:Urea / Q000008:administration & dosage* / Q000737:chemistry / Q000494:pharmacology
chemical_list: D014508:Urea