Effects of soap-water wash on human epidermal penetration

J Appl Toxicol. 2016 Aug;36(8):997-1002. doi: 10.1002/jat.3258. Epub 2015 Nov 15.


Skin decontamination is a primary interventional method used to decrease dermal absorption of hazardous contaminants, including chemical warfare agents, pesticides and industrial pollutants. Soap and water wash, the most common and readily available decontamination system, may enhance percutaneous absorption through the "wash-in effect." To understand better the effect of soap-water wash on percutaneous penetration, and provide insight to improving skin decontamination methods, in vitro human epidermal penetration rates of four C(14) -labeled model chemicals (hydroquinone, clonidine, benzoic acid and paraoxon) were assayed using flow-through diffusion cells. Stratum corneum (SC) absorption rates of these chemicals at various hydration levels (0-295% of the dry SC weights) were determined and compared with the results of the epidermal penetration study to clarify the effect of SC hydration on skin permeability. Results showed accelerated penetration curves of benzoic acid and paraoxon after surface wash at 30 min postdosing. Thirty minutes after washing (60 min postdosing), penetration rates of hydroquinone and benzoic acid decreased due to reduced amounts of chemical on the skin surface and in the SC. At the end of the experiment (90 min postdosing), a soap-water wash resulted in lower hydroquinone penetration, greater paraoxon penetration and similar levels of benzoic acid and clonidine penetration compared to penetration levels in the non-wash groups. The observed wash-in effect agrees with the enhancement effect of SC hydration on the SC chemical absorption rate. These results suggest SC hydration derived from surface wash to be one cause of the wash-in effect. Further, the occurrence of a wash-in effect is dependent on chemical identity and elapsed time between exposure and onset of decontamination. By reducing chemical residue quantity on skin surface and in the SC reservoir, the soap-water wash may decrease the total quantity of chemical absorbed in the long term; however, the more immediate accelerated absorption of chemical toxins, particularly chemical warfare agents, may be lethal. Copyright © 2015 John Wiley & Sons, Ltd.

Keywords: percutaneous penetration; pesticide; skin decontamination; stratum corneum; wash-in effect.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Benzoic Acid / pharmacokinetics
  • Chemical Warfare Agents / pharmacokinetics
  • Clonidine / pharmacokinetics
  • Decontamination*
  • Dose-Response Relationship, Drug
  • Epidermis / drug effects*
  • Epidermis / metabolism
  • Humans
  • Hydroquinones / pharmacokinetics
  • Paraoxon / pharmacokinetics
  • Permeability
  • Skin / drug effects*
  • Skin / metabolism
  • Skin Absorption / drug effects*
  • Soaps / chemistry*
  • Soaps / pharmacokinetics


  • Chemical Warfare Agents
  • Hydroquinones
  • Soaps
  • Benzoic Acid
  • Clonidine
  • Paraoxon
  • hydroquinone