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.

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There was a mistake in the Fig. 3 caption (p. 1000) and figure citations in the third paragraph of the Results section (pp. 999-1000) of "Effects of soap-water wash on human epidermal penetration" (Zhu et al., 2016).The corrected Fig. 3 caption is as follows: Figure 3. Epidermal penetration curves of hydroquinone compared for soap-water wash at 30 min postexposure (n = 8) and non-wash (n = 4). Note that the penetration rate of non-wash group continuously increased during 90 min experiment, the soap-water wash group showed decreased penetration rate after washing at 30 min postdosing.The corrected figure citations are as follows:Figures 1-3 shows penetration fluxes of benzoic acid, paraoxon and hydroquinone, respectively. Non-wash groups of benzoic acid and paraoxon reached constant penetration rates after 30 min exposure ( Figs. 1 and 2). Without surface wash, the penetration rate of hydroquinone continuously increased until the end of the experiment (Fig. 3). Before decontamination, the soap-water wash group and nonwash group of the same chemical showed similar penetration curves. As a soap-water wash was applied 30 min postexposure, the penetration rate of hydroquinone gradually decreased and reached a significant lower level compared to its non-wash group 50 min postdosing (20 min post-decontamination; Fig. 3). The increased percentage dose of benzoic acid in receptor fluid was determined 30-60 min postdosing (0-30 min post-decontamination); 30 min after decontamination (60 min postdosing), less penetration was observed in the soap-water wash group compared to the nonwash group (Fig. 1). The "wash-in" peak for benzoic acid resulted in no significant difference in the total penetration amount of benzoic acid at the experiment end (Table 1). The penetration curve of paraoxon was accelerated by soap-water wash during the 90 min experimental period (Fig. 2) resulting in a significant higher total amount penetrated in receptor fluid compared to non-wash samples (Table 1). A limited level of clonidine (0.2%) penetrated through human epidermis in 90 min, and the skin wash at 30 min showed no effect on penetration flux (figure not shown).

Massage sometimes influences chemical penetration rates and should be studied thoroughly to clarify the mechanisms and factors involved in the possible enhancing effect. This will also reveal more insight regarding the skin's ability to act as a barrier to exogenous substances and its role in risk assessment. How ex vivo results translate to in vivo behaviors still requires further investigation.

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