Interactions of skin thickness and physicochemical properties of test compounds in percutaneous penetration studies

  • Simon C. Wilkinson
  • Wilfred J. M. Maas
  • Jesper Bo Nielsen
  • Laura C. Greaves
  • Johannes J. M. van de Sandt
  • Faith M. WilliamsEmail author
Original Article


Objectives: To determine the effect of skin thickness on the percutaneous penetration and distribution of test compounds with varying physicochemical properties using in vitro systems. Studies were carried out in accordance with OECD guidelines on skin absorption tests. Methods: Percutaneous penetration of caffeine (log P −0.01), testosterone (log P 3.32), propoxur (log P 1.52) (finite dose in ethanol to water vehicle ratio) and butoxyethanol (log P 0.83) (undiluted finite dose or as an infinite dose 50% [v/v] aqueous solution) through skin of varying thicknesses under occluded conditions was measured using flow through cells for 8–24 h. Saline (adjusted to pH 7.4) was used as receptor fluid, with BSA added for studies with testosterone and propoxur. Following exposure, the remaining surface dose was removed by swabbing and the skin digested prior to scintillation counting. Results: The maximum flux of caffeine was increased with decreasing skin thickness, although these differences were found to be non-significant. The presence of caffeine in the skin membrane was not altered by skin thickness. Maximum flux and cumulative dose absorbed of testosterone and butoxyethanol (in both finite and infinite doses) were markedly reduced with full thickness (about 1 mm thick) skin compared with split thickness skin (about 0.5 mm). Maximum flux of propoxur (dissolved in 60% ethanol) was clearly higher through skin of 0.71 mm than through skin of 1.36 mm, but no difference was found between 0.56 and 0.71 mm. The proportion of propoxur present in the membrane after 24 h increased significantly over the complete range of thicknesses tested (0.56–1.36 mm). Conclusions: A complex relationship exists between skin thickness, lipophilicity and percutaneous penetration and distribution. This has implications for risk assessment studies and for the validation of models with data from different sources.


OECD guideline 428 In vitro percutaneous penetration Lipophilicity 



This work was carried out with financial support from the Fifth Framework Programme of the European Commission as part of the project ‘Evaluation and prediction of dermal absorption of toxic chemicals’ (EDETOX, QLRT-2000-00196). Some of the data were presented as a poster at the Ninth International Perspectives in Percutaneous Penetration Conference held in La Grande Motte, April 2004. An abstract (Wilkinson et al. 2004) appeared in the proceedings.


  1. Beck H, Bracher M, Bartnik FG (1994) Percutaneous absorption of hair dyes: an interlaboratory comparison of in vivo and in vitro data with rat and pig. Toxicol In Vitro 7:305–312Google Scholar
  2. Bowman BT, Sans WW (1983) Determination of octanol-water partitioning coefficients (kow) of 61 organo-phosphorus and carbamate insecticides and their relationship to respective water solubility (s) values. J Environ Sci Health Part B-Pestic Contam Agric Wastes 18:667–683Google Scholar
  3. Clowes HM, Scott RC, Heylings JR (1994) Skin absorption: flow through or static diffusion cells. Toxicol In Vitro 8:827–830CrossRefGoogle Scholar
  4. Cnubben NHP, Elliott GR, Hakkert BC, Meuling WJA, van de Sandt JJM (2002) Comparative in vitro-in vivo percutaneous penetration of the fungicide ortho-phenylphenol. Regul Toxicol Pharmacol 35:198–202CrossRefPubMedGoogle Scholar
  5. Cronin MTD, Schultz TW (2003) Pitfalls in QSAR. Theochem J Mol Struct 622:39–51CrossRefGoogle Scholar
  6. Dick IP, Scott RC (1992) Pig ear as an in vitro model for human skin permeability. J Pharm Pharmacol 44:640–645PubMedGoogle Scholar
  7. Franz TJ (1975) Percutaneous absorption on the relevance of in vitro data. J Invest Dermatol 64:190–195CrossRefPubMedGoogle Scholar
  8. Hawkins GS, Reifenrath WG (1986) Influence of skin source, penetration cell fluid, and partition coefficient on in vitro skin penetration. J Pharm Sci 75:378–381PubMedCrossRefGoogle Scholar
  9. Jakasa I, Mohammadi N, Kruse J, Kesic S (2004) Percutaneous absorption of neat and aqueous solutions of 2-butoxyethanol in volunteers. Int Arch Occup Environ Health 77(2):79–84CrossRefPubMedGoogle Scholar
  10. Kemppainen BW, Reifenrath WG, Stafford RG, Mehta M (1991) Methods for in vitro skin absorption studies of a lipophilic toxin produced by red tide. Toxicology 66:1–17CrossRefPubMedGoogle Scholar
  11. Lee FW, Earl L, Williams FM (2001) Interindividual variability in the percutaneous penetration of testosterone through human skin in vitro. Toxicology 168:63Google Scholar
  12. Moser K, Kriwet K, Nail W, Kalia YN, Guy RH (2001) Passive skin penetration enhancement and its quantification in vitro. Eur J Pharm Biopharm 52:103–112CrossRefPubMedGoogle Scholar
  13. OECD (2000a) (Organisation for Economic Co-operation and Development) Guideline for the testing of chemicals. Skin absorption: in vitro method, Draft Guideline 428, December 2000Google Scholar
  14. OECD (2000b) (Organisation for Economic Co-operation and Development) Guideline for the testing of chemicals. Skin absorption: in vivo method, Draft Guideline 427, December 2000Google Scholar
  15. OECD (2000c) (Organisation for Economic Co-operation and Development) Draft guidance document for the conduct of skin absorption studies. OECD environment health and safety publications, Series on Testing and Assessment no. 28, December 2000Google Scholar
  16. OECD (2000d) (Organisation for Economic Co-operation and Development) Test Guidelines Program. Percutaneous absorption testing: is there a way to consensus? OECD document ENV/JM/TG(2000)5, April 2000, Paris, FranceGoogle Scholar
  17. OECD (2004) (Organisation for Economic Co-operation and Development) Guideline for the testing of chemicals. Skin absorption: in vitro method. Adopted 13 April 2004 OECD, ParisGoogle Scholar
  18. Reifenrath WG, Hawkins GS, Kurtz MS (1991) Percutaneous penetration and skin retention of topically applied compounds. J Pharm Sci 80:526–532PubMedCrossRefGoogle Scholar
  19. Riddick JA, Bunger WB, Sakano TK (1986) Organic solvents: physical properties and methods of purification, 4th edn. Wiley, New York, NY, p 1325Google Scholar
  20. van de Sandt JJM, Meuling WJA, Elliott GR, Cnubben NHP, Hakkert BC (2000) Comparative in vitro–in vivo percutaneous penetration of the pesticide propoxur. Toxicol Sci 58:15–22CrossRefPubMedGoogle Scholar
  21. van de Sandt JJM, van Burgsteden JA, Cage S, Carmichael PL, Dick I, Kenyon S, Korinth G, Larese GF, Limasset JC, Maas WJM, Montomoli L, Nielsen JB, Payan J-P, Robinson E, Sartorelli P, Schaller KH, Wilkinson SC, Williams FM (2004) In vitro predictions of skin absorption of caffeine, testosterone and benzoic acid: a multi-centre comparison study. Regul Toxicol Pharmacol 39:271–281CrossRefPubMedGoogle Scholar
  22. Wilkinson SC, Williams FM (2002) Effects of experimental conditions on absorption of glycol ethers through human skin in vitro. Int Arch Occup Environ Health 75:519–527CrossRefPubMedGoogle Scholar
  23. Wilkinson SC, Greaves LC, Williams FM (2002) Transdermal electrical resistance and absorption measurements in a flow through cell. In: Brain KR, Walters KA (eds) Perspectives in percutaneous penetration, vol 8B. STS Publishing, Cardiff (in press)Google Scholar
  24. Wilkinson SC, Maas WJM, Nielsen JB, Greaves LC, van de Sandt JJM, Williams FM (2004) Influence of skin thickness on percutaneous penetration in vitro. In: Brain KR, Walters KA (eds) Perspectives in percutaneous penetration, vol 9A. STS Publishing, Cardiff, p 83Google Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Simon C. Wilkinson
    • 1
    • 4
  • Wilfred J. M. Maas
    • 2
  • Jesper Bo Nielsen
    • 3
  • Laura C. Greaves
    • 1
  • Johannes J. M. van de Sandt
    • 2
  • Faith M. Williams
    • 1
    Email author
  1. 1.School of Clinical and Laboratory SciencesUniversity of NewcastleNewcastle upon TyneUK
  2. 2.Physiological Sciences DepartmentTNO Nutrition and Food ResearchZeistThe Netherlands
  3. 3.Environmental Medicine, Institute of Public HealthUniversity of Southern DenmarkOdense CDenmark
  4. 4.Chemical Hazards and Poisons Division (Newcastle), Wolfson UnitHealth Protection AgencyNewcastle upon TyneUK

Personalised recommendations