title: What determines skin sensitization potency-myths, maybes and realities. Part 1. The 500 molecular weight cut-off.
abstract: BACKGROUND
  It is widely accepted that there is a molecular weight (MW) cut-off of 500, such that single chemicals with MWs higher than 500 cannot be skin sensitizers. If true, this could serve as a useful principle for designing non-sensitizing chemicals.
  
  
  OBJECTIVE
  To assess whether the 500 MW cut-off is a myth or a reality.
  
  
  METHODS
  A database of 699 chemicals tested for skin sensitization in guinea pigs or mice was analysed to establish the number of tested chemicals with MW > 500, and to establish whether any of these were sensitizers.
  
  
  RESULTS
  Only 13 (2%) of the 699 chemicals in the database have MW > 500. Of the 13 tested compounds with MW > 500 in the database, five are sensitizers and eight are non-sensitizers.
  
  
  CONCLUSIONS
  The 500 MW cut-off for skin sensitization is a myth, probably derived from the widespread misconception that ability to efficiently penetrate the stratum corneum is a key determinant of sensitization potency. The scarcity of sensitizers with MW > 500 simply reflects the general scarcity of chemicals with MW > 500.
authors.affiliation: School of Pharmacy and Chemistry, Liverpool John Moores University, Liverpool L3 3AF, UK. d.w.roberts@ljmu.ac.uk
authors.forename: David W
authors.initials: DW
authors.lastname: Roberts
authors.forename: Ovanes G
authors.initials: OG
authors.lastname: Mekenyan
authors.forename: Sabcho D
authors.initials: SD
authors.lastname: Dimitrov
authors.forename: Gergana D
authors.initials: GD
authors.lastname: Dimitrova
mesh_terms: D000485:Allergens / Q000737:chemistry* / Q000276:immunology; D000818:Animals; D016208:Databases, Factual; D017449:Dermatitis, Allergic Contact / Q000276:immunology*; D006168:Guinea Pigs; D051379:Mice; D008970:Molecular Weight
chemical_list: D000485:Allergens