For 20 years, using the replica method, we have evaluated the skin irritancy of about 10,000 commercial products which come into contact with the skin. In this method, test substances are usually applied on the flexor side of the upper arm for 24 h by semi-open patch test. Subsequently, skin replicas are taken and skin irritancy is evaluated microscopically. In the semi-open patch test, test substances are not completely occluded as in the closed patch test. Thus, this method is less invasive than the closed patch test method to the tested subjects. In this study, we investigated the sensitivity of microscopic scoring (MS) of the replica and visual scoring (VS) of the skin. Sodium lauryl sulphate (SLS) at 0.02%, 0.05%, and 0.2% was applied on 20 subjects' upper arms, using closed and semi-open methods. In both the closed patch test and the semi-open patch test, the value of MS correlated with the concentration of SLS, while VS did not show such a clear correlation. In addition, we compared 2 clinical tests for skin irritancy which are commonly performed in Japan: VS of 48 h closed patch test reaction on the subjects' upper backs and MS of 24 h semi-open patch test reaction on the subjects' upper arms (replica method). MS on the upper arms resulted in a constant score, regardless of the location of application, while VS on the upper back produced results which differed widely depending on the location. Thus, the replica method is a useful clinical test for skin irritancy, because it is sensitive, reproducible and non-invasive.

Japanese lacquer is made from the sap of the Japanese lacquer tree (Toxicodendron vernicifluum), a member of the Anacardiacae plant family. Objects painted with this material are described collectively as lacquerware. Both fresh lacquer and lacquerware may evoke allergic contact reactions ascribable to the urushiols contained therein. In this study, we have examined the effects of heating on the ability of lacquerware to elicit an allergic contact reaction. Lacquer films prepared with and without heat treatment were tested on urushiol-sensitive subjects. Patch test reactions were strongest to untreated film and decreased with increasing level of heat treatment. Assays for free urushiol in the lacquer films demonstrated that free urushiol content decreased with increasing heat treatment and that urushiols with saturated and monounsaturated alk(en)yl chains predominated.

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