title: Does epidermal turnover reduce percutaneous penetration?
abstract: OBJECTIVE
  After its removal from the skin surface, chemical remaining within the skin can become systemically available. The fraction of chemical in the skin that eventually enters the body depends on the relative rates of percutaneous transport and epidermal turnover (i.e., stratum corneum desquamation). Indeed, some investigators have claimed that desquamation is an efficient mechanism for eliminating dermally absorbed chemical from the skin.
  
  
  METHODS
  The fate of chemical within the skin following chemical contact was examined using a mathematical model representing turnover of and absorption into the stratum corneum and viable epidermis. The effects of turnover rate, exposure duration, penetrant lipophilicity, and lag time for chemical diffusion were explored.
  
  
  RESULTS
  These calculations show that significant amounts of chemical can be removed from skin by desquamation if epidermal turnover is fast relative to chemical diffusion through the stratum corneum. However, except for highly lipophilic and/or high molecular weight (>350 Da) chemicals, the normal epidermal turnover rate is not fast enough and most of the chemical in the skin at the end of an exposure will enter the body.
  
  
  CONCLUSIONS
  Epidermal turnover can significantly reduce subsequent chemical absorption into the systemic circulation only for highly lipophilic or high molecular weight chemicals.
authors.affiliation: Chemical Engineering and Petroleum Refining Department, Colorado School of Mines, Golden, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Reddy
authors.forename: R H
authors.initials: RH
authors.lastname: Guy
authors.forename: A L
authors.initials: AL
authors.lastname: Bunge
mesh_terms: D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism*; D006801:Humans; D008432:Mathematical Computing; D008954:Models, Biological; D010599:Pharmacokinetics; D012869:Skin Absorption / Q000502:physiology*